Selective Flocculation Enhanced Magnetic Separation of ... - MDPI

minerals Article

Selective Flocculation Enhanced Magnetic Separation of Ultrafine Disseminated Magnetite Ores Tao Su 1 , Tiejun Chen 1,2,3, *, Yimin Zhang 1,2,3 and Peiwei Hu 1,2,3 1 2 3

*

College of Resource and Environment Engineering, Wuhan University of Science and Technology, Wuhan 430081, China; [email protected] (T.S.); [email protected] (Y.Z.); [email protected] (P.H.) Hubei Key Laboratory for Efficient Utilization and Agglomeration of Metallurgic Mineral Resources, Wuhan 430081, China Hubei Collaborative Innovation Center for High Efficient Utilization of Vanadium Resources, Wuhan 430081, China Correspondence: [email protected]

Academic Editor: Kota Hanumantha Rao Received: 13 May 2016; Accepted: 12 August 2016; Published: 23 August 2016

Abstract: Simple magnetic separation for a certain magnetite mine with ultrafine disseminated lean ores has resulted in low performance, as the fine sizes and aggregation of ground mineral particles have caused inefficient recovery of the ultrafine minerals. In this study, we attempt to increase the apparent sizes of target mineral particles, and improve the separation indices, by using a multi-stage grinding-dispersion-selective flocculation-weak magnetic separation process. The results showed that under the conditions of 500 g/t sodium hexametaphospate (SHMP) as dispersant, 750 g/t carboxymethyl starch (CMS) as flocculant, agitating at 400 rpm for 10 min, with slurry pH 11, and final grinding fineness of 93.5% less than 0.03 mm, the obtained concentrate contained 62.82% iron, with recovery of 79.12% after multi-stage magnetic separation. Compared to simple magnetic separation, the concentrate’s iron grade increased by 1.26%, and a recovery rate by 5.08%. Fundamental analysis indicated that, in a dispersed state of dispersion, magnetite particles had weaker negative surface charges than quartz, allowing the adsorption of negative CMS ions via hydrogen bonding. Consequently, the aggregate size of the initial concentrate increased from 24.30 to 38.37 µm, accomplishing the goal of selective flocculation, and increasing the indices of separation. Keywords: magnetite; ultrafine dissemination; magnetic separation; selective flocculation

1. Introduction Hematite and magnetite are the two main minerals in China’s numerous iron ore sources. As easily processed mineral resources become depleted, iron ores that are low-grade, fine or mixed, and generally difficult to separate have become our current focus of research and exploitation [1,2]. This includes ultrafine disseminated iron ores [3], where the target minerals are largely disseminated at a −0.045 mm level, and fine grinding is needed to liberate. However, ultrafine fine mineral particles often lead to severe slime coating issues, contributing to unfavorable separation performance using traditional separation processes [4,5]. Much work has been done on the beneficiation of ultrafine disseminated hematite, and different separation techniques have been developed, e.g., hydrophobic and selective flocculation, The selective flocculation-desliming-flotation process has been successfully adopted in industrial practice [6,7]. In this process, separation is achieved by using polymer reagents’ adsorptive and connective effect to flocculate target minerals in the highly dispersed slurry, while leaving gangue minerals in suspension [8,9].

Minerals 2016, 6, 86; doi:10.3390/min6030086

www.mdpi.com/journal/minerals

Minerals 2016, 6, 86

2 of 12

The beneficiation of ultrafine disseminated magnetite also suffers from ultrafine particles, low relative susceptibility and poor performance. Current work on such minerals has been limited to the optimization of conventional processes. For example, a certain ultrafine disseminated magnetite mine in Qinghai, China evaluated the separation process of multi-stage grinding-multi-stage magnetic separation-combined direct/indirect flotation of concentrate, the obtained concentrate contained 60.11% iron, with 60.20% recovery, when the final grinding fineness is −0.030 mm at 80% [10]. Some mines in Liaoning, China tested with a multi-stage grinding-multi-stage separation process, with the obtained concentrate contained 63.29% iron, with 69.42% recovery, when the final grinding fineness is −0.074 mm at 99.38% [11]. The latter process, although simple and short, still fails to resolve the core issues of the target minerals lost to tailings, aggregation of particles, and its final performance below the expectation. In this study, we use polymeric selective flocculation to improve the performance of the beneficiation process of an ultrafine disseminated magnetite mine in Gansu, China, and examine the variations in fineness and surface properties of mineral particles before and after flocculation. The obtained results could provide useful information on the optimization of similar magnetic separation processes. 2. Characterization of the Raw Ore 2.1. Composition and Relative Concentration The main chemical components of the ore are shown in Table 1, and the mineral components shown in Table 2. Table 3 shows the distribution of chemical iron phases. Table 1. Main chemical components of raw ores. Component

TFe

SiO2

Al2 O3

FeO

CaO

MgO

S

P

Amount %

28.36

43.02

5.51

13.45

1.67

2.03

0.02

0.26

Table 2. Mineral components of raw ores. Mineral

Magnetite

Siderite

Hematite

Quartz

Feldspar

Dolomite

Sericite

Ankerite

Calcite

Amount %

33.8

2.4

1.5

28.7

10.4

7.8

3.2

3.7

2.7

Table 3. Fitting results for each binding energy peak. C Chemical State BE (eV)

C–C/C–H

C–O

O=C–O

284.73

286.54

288.85

It can be seen from Table 1 that the raw ore has a total iron grade of 28.36%, with low concentrations of sulfur and phosphorus (at 0.02% and 0.26%), and a high SiO2 content at 43.02%. Table 2 shows that the ores main metallic mineral is magnetite, with some siderite and hematite. The main gangue mineral is quartz, accounting for 28.7% of the total minerals. Other gangue minerals include feldspar, ankerite, dolomite, etc. Table 2 also shows that the iron content largely occurs as magnetite, with a distribution ratio of 88.75%, with some remaining iron in the forms of siderite, hematite, pyrite and iron silicate, making this a low-grade magnetite ore. 2.2. Dissemination of Main Minerals In order to obtain the particle size and combination characteristics of main minerals, a DMLP polarizing microscope (Leica Microsystems GmbH, Wetzlar, Germany) with both reflected and


3 of 12

transmitted light was used to examine the dissemination of magnetite and quartz in the ore. The sample prepared to 6,test Minerals 2016, 86 was crashed to −3 mm. The results are shown in Figure 1. 3 of 12


3 of 12

Figure 1. Optical microscope images of simples.

Figure 1. Optical microscope images of simples. Magnetite: the main ferrous mineral of the ore, occurring as euhedral and semi-euhedral fine grains that disseminated or denselyofdisseminated in gangue as minerals, withand occasional Magnetite: the are main ferrous mineral the ore, occurring euhedral semi-euhedral metasomatism at the edges by hematite; its distribution is non-uniform dissemination of largely fine fine grainsgrains, thatthe arefineness disseminated or densely disseminated in gangue minerals, with occasional size is below 0.1 mm; particularly, 90% of the grains are of fineness −0.038 mm metasomatism at the edges by hematite; itsmicroscope distribution dissemination of largely Figure 1. Optical imagesisofnon-uniform simples. and 99% −0.074 mm. the size main is gangue mineral, withparticularly, occasional coarse or in joint fine grains, theQuartz: fineness below 0.1 mm; 90%grains, of thegenerally grains scattered, are of fineness −0.038 mm Magnetite: the mainultrafine ferrous mineral ofaggregated the ore, occurring as euhedral and semi-euhedral fine adhesion with feldspar; quartz in grains or veins are common; dissemination is and 99% −0.074 mm. grains are disseminated or size densely disseminated gangue minerals, occasional highlythat non-uniform, the fineness is below 0.15 mm; in particularly, 50% of thewith grains are of Quartz: the mainatmm gangue mineral, with occasional coarse grains, generally scattered, or in joint metasomatism the and edges by−0.074 hematite; fineness −0.038 87% mm.its distribution is non-uniform dissemination of largely fine adhesiongrains, withThe feldspar; quartz inminerals aggregated grains or grains veins are dissemination is the fineness size is below 0.1 mm; particularly, 90% of the ofcommon; fineness −0.038 mm primaryultrafine ferrous and gangue are ultrafine grains in aare complex disseminative relationship, which classifiessize the is orebelow as an 0.15 ultrafine disseminated, lean50% magnetite with are highof fineness and 99% −0.074the mm. highly non-uniform, fineness mm; particularly, of the ore grains difficulty ofthe separation. Quartz: −0.038 mm and 87% −main 0.074gangue mm. mineral, with occasional coarse grains, generally scattered, or in joint adhesion with feldspar; ultrafine quartz in aggregated grains or veins are common; dissemination is The primary ferrous and gangue minerals are ultrafine grains in a complex disseminative 2.3. Test Methods highly non-uniform, the fineness size is below 0.15 mm; particularly, 50% of the grains are of relationship, which classifies the−0.074 ore mm. as an ultrafine disseminated, lean magnetite ore with high fineness −0.038Magnetic mm and Separation 87% 2.3.1. Simple Process difficulty of separation. The primary ferrous and gangue minerals are ultrafine grains in a complex disseminative The test device is a low-intensity magnetic drum separator (Changsha Research Institute of relationship, which classifies the ore as an ultrafine disseminated, lean magnetite ore with high Mining And Metallurgy, Changsha, China). The process includes an initial grinding and separation, 2.3. Test Methods difficulty of separation. a discard of tailings, and a second grinding and separation. The optimal grinding fineness and strength of magnetic field are determined by prior testing. The workflow is shown in the part of 2.3. Test Methods Separation Process 2.3.1. Simple Magnetic Figure 2 marked by dotted lines. 2.3.1. Simple Magnetic Separation Process

The test device is a low-intensity magnetic drum separator (Changsha Research Institute of test deviceChangsha, is a low-intensity magnetic drum separator (Changsha Institute of Mining AndThe Metallurgy, China). The process includes an initialResearch grinding and separation, Mining And Metallurgy, Changsha, China). The process includes an initial grinding and separation, a discard of tailings, and a second grinding and separation. The optimal grinding fineness and strength a discard of tailings, and a second grinding and separation. The optimal grinding fineness and of magnetic field are determined by prior testing. The workflow is shown in the part of Figure 2 strength of magnetic field are determined by prior testing. The workflow is shown in the part of marked by dotted lines.by dotted lines. Figure 2 marked

Figure 2. The flow-sheet of process.

Figure Theflow-sheet flow-sheet ofof process. Figure 2.2.The process.


4 of 12

2.3.2.Minerals Selective Separation Process 2016, Flocculation-Magnetic 6, 86

4 of 12

The process includes dispersion, selective flocculation, and weak magnetic separation. The 2.3.2. Selective Flocculation-Magnetic Separation Process grinding fineness and magnetic strength are unchanged. The workflow is shown in the part of Figure 2 The process includes dispersion, selective flocculation, and weak magnetic separation. The marked by solid lines. grinding fineness and magnetic strength are unchanged. The workflow is shown in the part of (a) Dispersion Tests Figure 2 marked by solid lines. The (a) finely ground slurry is diluted to 15 wt %, with dispersant added, and pH adjusted (using Dispersion Tests HCl and The NaOH), for 5ismin at the speed 800–1000 r/min, and for 10(using min. The finely agitated ground slurry diluted to 15 wt %,of with dispersant added, andsettled pH adjusted sediment is weighed, and the dispersion is calculated using the following equation: HCl and NaOH), agitated for 5 min at the speed of 800–1000 r/min, and settled for 10 min. The sediment is weighed, and the dispersion is calculated using the following equation:

Dispersion =

Total specimen weight − Sediment weight after 10min × 100%; Total specimen weight − Sediment weight after 10min Total specmen weight ×100%

Dispersion =

Total specmen weight

;

(1) (1)

(b) Flocculation Tests (b) Flocculation Tests The dispersed slurry is placed in a mixer, with flocculants added and pH adjusted (using HCl The dispersed slurry is placed in a mixer, with flocculants added and pH adjusted (using HCl and NaOH), andand with 5–10 drops Themixture mixture agitated 10 min at speed of and NaOH), with 5–10 dropsofofkerosene kerosene added. added. The is is agitated for for 10 min at speed of 200–1000 r/min before magnetic theresults resultsofofseparation separation indices are analyzed. 200–1000 r/min before magneticseparation, separation, and and the indices are analyzed. 3. Test Results andand Analysis 3. Test Results Analysis 3.1. Simple Magnetic Separation Tests 3.1. Simple Magnetic Separation Tests The optimal process andand its conditions have been tests,with with the The optimal process its conditions have beendetermined determined by by early early exploratory exploratory tests, the final parameters and indicators shown in Figure 3. final parameters and indicators shown in Figure 3.

Figure 3.The quantity-quality flow-sheet flow-sheet ofofsimple magnetic separation. Figure 3. The quantity-quality simple magnetic separation.

It can be seen that the simple process can obtain concentrate containing 61.54% iron, with

It can berecovery seen thatfrom the simple can obtain concentrate iron, with 74.04% 74.04% the rawprocess magnetite ore. While the ironcontaining grade can 61.54% meet the industrial recovery from the the rawrecovery magnetite While thedesired. iron grade can meet the industrial requirements, rateore. is less than The weight changes show thatrequirements, 10.41% and the 15.55% lost to tailings and II, changes respectively, correspond 4.47%ofand 11.39% recovery rateofisiron lessare than desired. TheIweight showwhich that 10.41% and to 15.55% iron are lost to occurrences in the raw ore. Since the lost iron in tailings II has a higher grade and loss rate, andSince tailings I and II, respectively, which correspond to 4.47% and 11.39% occurrences in the raw ore. accounts for a larger proportion of the ore, the study will focus on analyzing tailings II to find out theof the the lost iron in tailings II has a higher grade and loss rate, and accounts for a larger proportion cause of lost iron, and take measures to increase the recovery rate. ore, the study will focus on analyzing tailings II to find out the cause of lost iron, and take measures to increase the recovery rate.


5 of 12


5 of 12

Figure 4 shows the results of Scanning Electronic Microscopy (SEM, Philips, Amsterdam, Figure Minerals 2016, 6,486shows the results of Scanning Electronic Microscopy (SEM, Philips, Amsterdam, 5 of 12 The Netherlands) andand Electron Probe Microanalysis TheNetherlands) Netherlands) on The Netherlands) Electron Probe Microanalysis(EPMA, (EPMA,Philips, Philips, Amsterdam, Amsterdam, The on II. tailings SEMthat shows that octahedral particles occur frequently in tailings II, which Figure 4 shows theoctahedral results of particles Scanning Electronic Microscopy (SEM, Amsterdam, tailings SEM II. shows occur frequently in tailings II,Philips, which when when combined with of EPMA results Probe of micro-zones 1 and provenAmsterdam, toMagnetite be magnetite. Magnetite The Netherlands) and Electron Microanalysis (EPMA, Philips, The Netherlands) with combined EPMA results micro-zones 1 and 2, are proven to2,beare magnetite. generally occurs as generally occurs as singular particles, such as particles those in and micro-zones 1, 2, and but seen some are alsowhen seen with on tailings II. such SEM shows that occur frequently in 6, tailings II, aggregated which singular particles, as those in octahedral micro-zones 1, 2, 6, but some are also aggregated with gangue minerals, as micro-zone magnetite below in combined with EPMA results of such micro-zones 1 and5.Ultrafine 2, are proven to beparticles magnetite. Magnetite gangue minerals, such as micro-zone 5.Ultrafine magnetite particles below 5 µm in size are5 μm commonly size are commonly sighted, e.g., in micro-zones 1, 2, and 4, and 1, occasionally generally occurs as singular particles, such as those in3, micro-zones 2, and 6, butthere someare aremagnetite also seen sighted, e.g., in micro-zones 1, 2, 3, and 4, and occasionally there are magnetite particles below 10 µm, particles below μm, e.g., micro-zone can be concluded that magnetite a significant amount of magnetite aggregated with10gangue minerals, such6.asItmicro-zone 5.Ultrafine particles below 5 μm in e.g., micro-zone 6. It can beduring concluded that a significant amount ofoccasionally magnetite has been lost to tailings has lost to tailings theinbeneficiation, the4,final indices, may be sizebeen are commonly sighted, e.g., micro-zones affecting 1, 2, 3, and andseparation there which are magnetite during the beneficiation, affecting the final separation indices, which may be caused by these particles caused these10particles finer 6. than thebeminimum of theamount device, oformagnetite by their particlesby below μm, e.g.,being micro-zone It can concludedcapabilities that a significant beingaggregation finer than the minimum capabilities of the device, or by their aggregation with gangue minerals. gangue minerals. has been lostwith to tailings during the beneficiation, affecting the final separation indices, which may be caused by these particles being finer than the minimum capabilities of the device, or by their aggregation with gangue minerals.

Figure 4. Scanning Electronic Microscopy (SEM) and Electron Probe Microanalysis (EPMA) analysis

Figure 4. Scanning Electronic Microscopy (SEM) and Electron Probe Microanalysis (EPMA) analysis on tailings II. on tailings II. Figure 4. Scanning Electronic Microscopy (SEM) and Electron Probe Microanalysis (EPMA) analysis

Cumulative undersize/% Cumulative undersize/%

Figure 5 shows the particle size distributions of the finely ground initial concentrate, the final on tailings II. concentrate, and tailings II. As can seen, the finelyofground initialground concentrate hasconcentrate, particularly finer Figure 5 shows the particle sizebedistributions the finely initial the final particles, with 88.31% atdistributions −25the μm, and 35.24% atground −5 μm. Afterconcentrate, separation, mineral Figure 5tailings shows the sizeseen, of ground the finely initial the final finer concentrate, and II.ofparticle Asminerals can be finely initial concentrate has particularly particles μm only accounts 9.68% of35.24% theground final concentrate, while as as 47.1% of concentrate, and5tailings II. As can seen, the finely initial hasmuch particularly finer particles, withbelow 88.31% of minerals at −be25for µm, and at − 5 µm.concentrate After separation, mineral particles tailings II are 5 μm. are at reasons to believe that most fineμm. magnetite particles have been particles, withbelow 88.31% of There minerals −25 μm, and 35.24% at −5 After separation, mineral below 5 µm only accounts for 9.68% of the final concentrate, while as much as 47.1% of tailings II lost to tailings the separation, leading [12]. while This isasconsistent particles belowduring 5 μm only accounts for 9.68% to of the thelow finalrecovery concentrate, much as with 47.1%the of are below 5 µm. There are reasons to believe that most fine magnetite particles have been lost to results analysis. tailingsofII SEM are below 5 μm. There are reasons to believe that most fine magnetite particles have been tailings during the separation, leading to the low recovery [12]. This is consistent with the results of lost to tailings during the separation, leading to the low recovery [12]. This is consistent with the SEM results analysis. of SEM analysis. 47.1% 100 80 100

35.24% 47.1%

60 0um 80

9.68%

40 60 0um 20 40

9.68%

0 20 0.1

5um

35.24%

5um

1

Rough Concentrate Concentrate TailingsⅡ 10 Rough Concentrate 100 Concentrate TailingsⅡ

Size/um 0 Figure0.1 5. The particle1 size distributions of products. 100 Size/um 10

Figure Theparticle particle size size distributions Figure 5. 5.The distributionsofofproducts. products.

Minerals 2016, 6, 86 Minerals 2016, 6, 86

6 of 12 6 of 12


6 of 12

3.2. Tests 3.2. Selective Selective Flocculation-Magnetic Flocculation-Magnetic Separation Separation Tests 3.2. Selective Flocculation-Magnetic Separationultra Tests Having the simple simple Having reached reached the the conclusion conclusion that that ultra fine fine mineral mineral particles particles are are the the cause cause of of the separation process’s low performance, we a polymeric selective separation process’s performance, we a fine polymeric selective flocculation-magnetic separation Having reachedlow the conclusion thatadopt ultraadopt mineral particles are theflocculation-magnetic cause of the simple separation process, in hope of reducing aggregation between target minerals and gangue minerals, process, in hope of reducing aggregation between targeta minerals andselective gangue minerals, increasing the separation process’s low performance, we adopt polymeric flocculation-magnetic increasing the apparent sizesofofreducing target mineral particles, and theindices. performance apparent sizes of target mineral particles, and improving the improving performance separation process, in hope aggregation between target minerals and gangueindices. minerals, increasing the apparent sizes of target mineral particles, and improving the performance indices. 3.2.1. Dispersion Tests 3.2.1.Good Dispersion Tests of minerals in water is an important prerequisite for successful selective dispersion hexametaphosphate (SHMP), sodium silicate (SS), flocculation. The dispersion tests utilized sodium (SHMP), silicate (SS), Good dispersion of minerals in water is anhexametaphosphate important prerequisite for sodium successful selective NaOH to study the effect of dispersants and their dosages. For SHMP and SS, the slurry has a pH and NaOH to study the effect of dispersants and their dosages. For SHMP and SS, the slurry has a flocculation. The dispersion tests utilized sodium hexametaphosphate (SHMP), sodium silicate (SS), of 10–11. The results are shown Figure 6. 6. pH of 10–11. results are shown in Figure and NaOH toThe study the effect ofindispersants and their dosages. For SHMP and SS, the slurry has a pH of 10–11. The results are shown in Figure 6. 36

SHMP SS NaOH SHMP

36 30

SS NaOH

Dispersion/% Dispersion/%

30 24 24 18 18 12 126 60 0

0 0

250

500 750 Dispersant dosage (g/t) 250 500 750 Dispersant dosage (g/t)

1000 1000

Figure 6. The effect of dispersants and their amounts. Figure 6. The effect of dispersants and their amounts.

It It can can be be seen seen in in Figure Figure 66 that, that, as as the the amounts amounts of of dispersing dispersing agents agents increase, increase, the the dispersion dispersion rates rates first increase greatly, then tend toward stabilization. The dispersion effectiveness of the agents, It can begreatly, seen inthen Figure 6 that, as the amounts of dispersing agents increase,ofthe rates first increase tend toward stabilization. The dispersion effectiveness thedispersion agents, ranking ranking from highare: to low are: SHMP, SS,stabilization. and SHMP NaOH.has SHMP has the best effect when applied at first greatly, then tend toward The dispersion effectiveness of the agents, fromincrease high to low SHMP, SS, and NaOH. the best effect when applied at 500 g/t, 500 g/t, resulting in to an low increase dispersion rate fromto6.54% to has 27.85%. ranking from are: in SHMP, SS, and NaOH. SHMP the best effect when applied at resulting in anhigh increase in dispersion rate from 6.54% 27.85%. With SHMP at 500 g/t, we tested the effect of slurry pH on dispersion rate, with results shown 500 g/t, resulting in 500 an increase in dispersion rate 27.85%. rate, With SHMP at g/t, we tested the effect of from slurry6.54% pH ontodispersion with results shown in in Figure 7. With Figure 7. SHMP at 500 g/t, we tested the effect of slurry pH on dispersion rate, with results shown 36

in Figure 7.

Dispersion/% Dispersion/%

36 30 30 24 24 18 18 12 12 6 6 0

10.0

10.5

11.0

11.5 12.0 12.5 13.0 pH 10.0 10.5 11.0 11.5 12.0 12.5 13.0 Figure 7. Dispersion rate pH at different slurry pH. 0

Figure Figure 7. 7. Dispersion Dispersion rate rate at at different different slurry slurry pH. pH.

As can be seen in Figure 7, the slurry’s dispersion rate shows a remarkable increase when its pH increases from 10 toin 11,Figure then tends when its pH continues to increase. Therefore As can be seen 7, the toward slurry’sstabilization dispersion rate shows a remarkable increase when its pH As can be seen in Figure 7, the slurry’s dispersion rate shows a remarkable increase when its pH the optimal slurry pH is determined to be 11. increases from 10 to 11, then tends toward stabilization when its pH continues to increase. Therefore increases from 10 to 11, then tends toward stabilization when its pH continues to increase. Therefore Next, measurements were made the surface potentials of magnetite and quartz minerals the optimal slurry pH is determined to on be 11. the optimal slurry pH is determined to be 11. under different conditions, for analysis of thesurface mechanism through which SMHP pHminerals affected Next, measurements were made on the potentials of magnetite and and quartz Next, measurements were made on the surface potentials of magnetite and quartz minerals under dispersion using DLVO theory. under different conditions, for analysis of the mechanism through which SMHP and pH affected different conditions, for analysis of the mechanism through which SMHP and pH affected dispersion As shown Figuretheory. 8, both increasing the slurry’s pH and the addition of SHMP can cause the dispersion usinginDLVO using DLVO theory. zeta As potential of magnetite andincreasing quartz particles to decrease. This is dueoftoSHMP the solid particles shown in Figure 8, both the slurry’s pH and the addition can cause the − adsorbing the introduced OHand or the phosphate radicals ionized from According classical zeta potential of magnetite quartz particles to decrease. This SHMP. is due to the solidto particles adsorbing the introduced OH− or the phosphate radicals ionized from SHMP. According to classical


7 of 12

Minerals 6,6,86 As2016, shown Minerals 2016, 86in

77of Figure 8, both increasing the slurry’s pH and the addition of SHMP can cause the of12 12 zeta potential of magnetite and quartz particles to decrease. This is due to the solid particles adsorbing −stable DLVO theory, dispersion ofofradicals the mineral particle system DLVO theory,the thestable dispersion theultrafine ultrafine mineral particleAccording systemisismoderated moderated bythe the the introduced OH or the phosphate ionized from SHMP. to classical by DLVO equilibrium between the attractive van der Waals force and the repulsive double layer force, and the equilibrium between the attractive van der mineral Waals force and system the repulsive double by layer and the theory, the stable dispersion of the ultrafine particle is moderated theforce, equilibrium latter the square particle charge. Thus, the ofof pH latter isis proportional proportional the square particle surface charge. Thus,layer the increase increase pHand and the the between the attractivetoto van der Waalsofofforce andsurface the repulsive double force, and the latter is addition of SHMP could decrease the zeta potential and increase the negative charges on particle addition of SHMP could decrease thesurface zeta potential and increase the negative charges on particle proportional to the square of particle charge. Thus, the increase of pH and the addition of surfaces, causing the rate totoincrease. ItItcan be from surfaces, causing theslurry’s slurry’s dispersion rate increase. canalso also benoted noted fromFigure Figure77that, that,for for SHMP could decrease the zeta dispersion potential and increase the negative charges on particle surfaces, causing slurry pH higher than 8, quartz is still more negatively charged than magnetite after adding SMHP, slurry pH higher than 8, quartz is still more negatively charged than magnetite after adding SMHP, the slurry’s dispersion rate to increase. It can also be noted from Figure 7 that, for slurry pH higher which provided aa favorable condition for selective flocculation ofof magnetite from silica, which provided favorable condition forthan selective flocculation magnetite from silica, as as than 8, quartz is still more negatively charged magnetite after adding SMHP, which provided a discussed below. discussedcondition below. for selective flocculation of magnetite from silica, as discussed below. favorable 4545 3030

Magnetite Quartz Magnetite Quartz Magnetite+SMHP Quartz+SMHP Magnetite+SMHP Quartz+SMHP

Zeta potential/mV Zeta potential/mV

1515 00

-15 -15 -30 -30 -45 -45 -60 -60 -75 -75 -90 -90

-105 -105

44

66

8 pH pH 8

1010

1212

Figure particles. Figure 8.8.The The zeta potential ofofmagnetite magnetite and quartz Figure8. Thezeta zetapotential potentialof magnetiteand andquartz quartzparticles. particles.

3.2.2. 3.2.2.Flocculation FlocculationTests Tests 3.2.2. Flocculation Tests Based on preliminary work on selective flocculation and flotation ofofultrafine ultrafine disseminated Basedon onpreliminary preliminarywork workon onselective selectiveflocculation flocculationand andflotation flotationof ultrafinedisseminated disseminated Based magnetite ores, the initial candidates for flocculants were carboxymethyl starch (CMS), sodium magnetiteores, ores, initial candidates for flocculants were carboxymethyl starch sodium (CMS),humate, sodium magnetite thethe initial candidates for flocculants were carboxymethyl starch (CMS), humate, and common corn starch. humate, and corn common corn starch. and common starch. The effects ofofflocculant flocculant types and amounts on concentrate indices were tested using magnetic Theeffects effectsof flocculanttypes typesand andamounts amountson onconcentrate concentrateindices indiceswere weretested testedusing usingmagnetic magnetic The separation at pH 10–11, agitated at 400 r/min for 10 min. The results are shown in Figure 9. separationatatpH pH10–11, 10–11,agitated agitatedatat400 400r/min r/min for for 10 10 min. min. The The results results are are shown shown in in Figure Figure9. 9. separation

8989

6464

8787

6363

8585

6262

CMS CMS Sodium Sodiumhumate humate Corn Cornstarch starch

8383 8181 7979 00

Grade/% Grade/%

6565

Recovery/% Recovery/%

9191

200 200

400 400 600 600 800 800 1000 1000 1200 1200 Reagent Reagentdosage(g/t) dosage(g/t)

(a) (a)

6161

CMS CMS Sodium Sodiumhumate humate Corn Cornstarch starch

6060 5959 0

0

200 200

400 400 600 600 800 800 1000 1000 1200 1200 Reagent Reagentdosage(g/t) dosage(g/t)

(b) (b)

Figure 9.9.The effects ofofflocculant on concentrate. (a) Iron recovery; (b) Iron grades. Figure The flocculanttypes typesand andamounts amountson onconcentrate. concentrate.(a) (a)Iron Ironrecovery; recovery;(b) (b) Iron grades. Figure 9. The effects effects of flocculant types and amounts Iron grades.

Figure Figure9a 9adepicts depictsthe theeffects effectsofofflocculant flocculanttypes typesand andamounts amountson oniron ironrecovery. recovery.As Asflocculants flocculants Figure 9a depicts the effects of flocculant types and amounts on iron recovery. As flocculants increase, increase,the therecovery recoverycould couldreach reachaamaximum. maximum.This Thisisisbecause becausetoo toolittle littleflocculant flocculantisisineffective, ineffective, increase, the recovery could reach a maximum. This is because too little flocculant is ineffective, while while whiletoo toomuch muchflocculant flocculantcauses causesexcessive excessiveadsorption adsorptionon onparticle particlesurfaces, surfaces,breaking breakingup upinitially initially too much flocculant causes excessive adsorption on particle surfaces, breaking up initially aggregated aggregated aggregatedcolloids, colloids,ininaaprocess processcalled called“colloid “colloidprotection” protection”[13] [13]or or“over-dosing” “over-dosing”effect. effect.Figure Figure9b 9b colloids, in a process called “colloid protection” [13] or “over-dosing” effect. Figure 9b shows the shows the effects of flocculant types and amounts on iron grades, which while less significant, still shows the effects of flocculant types and amounts on iron grades, which while less significant, still effects of flocculant types and amounts on iron grades, which while less significant, still display an display display an an increase increase over over the the results results without without flocculants. flocculants. This This increase increase isis due due toto the the flocculants flocculants increase over the results without flocculants. This increase is due to the flocculants impediment of impediment impedimentofofaggregation aggregationbetween betweendifferent differenttypes typesofofmineral mineralparticles. particles. aggregation between different types of mineral particles. Overall, Overall, the the best best effects effects on on concentrate concentrate indices indices are are reached reached atat 750 750 g/t g/t for for CMS, CMS, 500 500 g/t g/t for for sodium sodiumhumate, humate,and and1000 1000g/t g/tfor forcorn cornstarch. starch.


8 of 12

The effects of agitator speed were tested under the conditions of 750 g/t CMS, 500 g/t sodium humate, or 1000 g/t corn starch, using slurry pH 10–11 and agitation time 10 min. The results are shown2016, in Figure Minerals 6, 86 10. 8 of 12 Figure 10a depicts the effects of agitator speed on concentrate recovery rate, which are notable, and display similar trends for the flocculants. The recovery rates increase when the speed increases the r/min best effects on lower concentrate indices reached at 750 g/t for CMS, 500 g/t for between sodium fromOverall, 200 to 400 because speeds cannotare induce sufficient contact and adsorption humate, and 1000 g/t for corn starch. flocculants and magnetite particles. On the other hand, overly fast agitation can break up the formed of the agitator speed were tested under the conditions of 750 g/t CMS, 500 g/t sodium flocsThe andeffects disrupt flocculation process. humate, or 1000 g/t corn starch, using slurryspeed pH 10–11 andgrade, agitation time min. The results are Figure 10b shows the effects of agitation on iron which are10 less significant, varying shown in Figure 10. between the 61.5%–63% range. 91 89

63

87 85 83

62 61 60

81 79

CMS Sodium humate Corn starch

64

Grade/%

Recovery/%

65

CMS Sodium humate Corn starch

200

400 600 800 agitator speed(r/min)

59

1000

200

(a)

400

600 800 agitator speed(r/min)

1000

(b)

Figure10. 10.The Theeffects effectsofofagitator agitatorspeed speedon onconcentrate. concentrate.(a) (a)Iron Ironrecovery; recovery;(b) (b)Iron Irongrades. grades. Figure

Combining the results of dispersion and flocculation tests, it can be concluded that the optimal Figure 10a depicts the effects of agitator speed on concentrate recovery rate, which are notable, conditions are: SHMP at 500 g/t for the dispersant; CMS at 750 g/t for the flocculant; slurry pH at 11; and display similar trends for the flocculants. The recovery rates increase when the speed increases and agitation at 400 r/min for 10 min. The resultant concentrate has a grade of 62.82%, with an from 200 to 400 r/min because lower speeds cannot induce sufficient contact and adsorption between operational recovery rate of 88.31% and a total recovery rate of 79.12%. Compared to simple flocculants and magnetite particles. On the other hand, overly fast agitation can break up the formed magnetic separation, the iron grade has been increased by 1.26%, and the recovery rate increased flocs and disrupt the flocculation process. by 5.08%. Figure 10b shows the effects of agitation speed on iron grade, which are less significant, varying between the 61.5%–63% range. Mechanism 3.2.3. Analysis of Flocculation Combining the results of dispersion and flocculation tests, it can be concluded that the optimal In order analyze mechanism of the polymeric flocculant’s adsorption on mineral conditions are:toSHMP at the 500selective g/t for the dispersant; CMS at 750 g/t for the flocculant; slurry pH at surfaces, we conducted separate dispersion-selective the of initial concentrate, 11; and agitation at 400 r/min for 10 min. The resultantflocculation concentrate tests has aon grade 62.82%, with an pure magnetite minerals, and pure The fineness variations before and flocculation operational recovery rate of 88.31% andquartz. a total recovery rate of 79.12%. Compared to after simple magnetic using a laser fineness analyzer, with results in Figure 11. The magnetite minerals before and after separation, the iron grade has been increased by 1.26%, and the recovery rate increased by 5.08%. flocculation are rinsed with deionized water for infrared spectral analysis, shown in Figure 12. 3.2.3. Analysis of Flocculation Mechanism 100

Rough Concentrate

100

Quartz

Cum ulative undersize/ %

Cumulative undersize/%

In order toFlocculation analyze the selective mechanism of the polymeric flocculant’s adsorption on mineral Flocculation Quartz Rough Concentrate surfaces,80we conducted separate dispersion-selective flocculation tests on the initial concentrate, pure Magnetite 80 Flocculation Magnetite magnetite minerals, and pure quartz. The fineness variations before and after flocculation using a laser fineness60analyzer, with results in Figure 11. The magnetite 60 minerals before and after flocculation are rinsed with deionized water for infrared spectral analysis, shown in Figure 12. As 40 seen in Figure 11, the initial concentrate’s particle 40 sizes show a general trend of increase after flocculation, with the average size increasing by 57.90%, from 24.30 to 38.37 µm. The other minerals 20 20 flocculating After flocculating also show an increase, with pure Before magnetite’s average particle size increasing by Before 79.52% from 12.45 (D[4,3]/um) (D[4,3]/um) flocculating After flocculating (D[4,3]/um) Rough 24.3 38.37 to 22.35 µm, while pure quartz’s 7.97 12.45 to 8.97(D[4,3]/um) µm. This Magnetite 22.35 Concentrate average particle increases only by 7.53% from 0 Quartz 7.97 8.56 0 means that while CMS has flocculating effects on both magnetite and quartz, the effect is significantly 0.1 1 10 100 Size/um 0.1 1 10 100 Size/um biased toward magnetite. Thus, the selective flocculation of magnetite is the main cause of the initial (a) after flocculation. (b) concentrate’s fineness increase Figure the main absorption frequencies for the minerals are: theflocculation; Fe–O flexural Figure 12 11.shows (a) Thethat particle size distributions of rough concentrate before and after − 1 − 1 vibration absorption peak at band 1 (471 cm ) and (1080 cm ); the Fe–O stretching vibration (b) The particle size distributions of magnetite andband quartz3 before and after flocculation. peak at band 2 (543 cm−1 ); the –OH flexural vibration peak at band 4 (1400 cm−1 ) and band 6 (3445 cm−1 ); the COO–asymmetrical stretching vibration peak at band 5 (1624 cm−1 ) [14]. Here, the bands 4, 5, and 6 are absorption peaks of the CMS functional group. Thus, we know that adsorption of

conditions are: SHMP at 500 g/t for the dispersant; CMS at 750 g/t for the flocculant; slurry pH at 11; and agitation at 400 r/min for 10 min. The resultant concentrate has a grade of 62.82%, with an operational recovery rate of 88.31% and a total recovery rate of 79.12%. Compared to simple magnetic separation, the iron grade has been increased by 1.26%, and the recovery rate increased Minerals 2016, 6, 86 9 of 12 by 5.08%.

Transmittance/%

Cum ulative undersize/ %

Cumulative undersize/%

3.2.3. Analysis of Flocculation Mechanism CMS had occurred on the surfaces of magnetite particles. The adsorption between organic polymeric Minerals 6, 86 9 of 12 flocculants and generally depends attraction, van der Waalsonforce and In2016, order tomineral analyzeparticles the selective mechanism ofon theelectrostatic polymeric flocculant’s adsorption mineral hydrogen bonds. As the magnetite in this dispersion condition have surface charges, surfaces, we conducted separate particles dispersion-selective flocculation tests onnegative the initial concentrate, As seen in Figure 11,negative the initial concentrate’s show general trendattraction, of increase after the with the CMS ions should not besizes caused byaelectrostatic but by pureadsorption magnetite minerals, and pure quartz. Theparticle fineness variations before and after flocculation flocculation, with the average size increasing by Figure 57.90%, from 24.30 to 38.37 μm.7), The other minerals hydrogen bonding. Since magnetite is less negatively charged than silica (Figure the adsorption of using a laser fineness analyzer, with results in 11. The magnetite minerals before and after also show an increase, with pure magnetite’s average particle size increasing by 79.52% from 12.45 to CMS on magnetite by hydrogen bonding would more favored that shown on silica. flocculation are rinsed with deionized water for be infrared spectral than analysis, in Figure 12. 22.35 μm, while pure quartz’s average particle increases only by 7.53% from 7.97 to 8.97 μm. This means100 that while CMS has flocculating effects on100both Quartz magnetite and quartz, the effect is Rough Concentrate Flocculation Quartz Flocculation Rough ConcentrateThus, the selective flocculation significantly biased toward magnetite. of magnetite is the main cause Magnetite 80 80 of the initial concentrate’s fineness increase after flocculation. Flocculation Magnetite Figure 12 shows that the main absorption frequencies for the minerals are: the Fe–O flexural 60 60 3 (1080 cm−1); the Fe–O stretching vibration vibration absorption peak at band 1 (471 cm−1) and band −1 peak at band 2 (543 cm ); the –OH flexural vibration peak at band 4 (1400 cm−1) and band 6 40 40 (3445 cm−1); the COO–asymmetrical stretching vibration peak at band 5 (1624 cm−1) [14]. Here, the bands 4,205, and 6 are absorption peaks of the CMS functional group. Thus, we know that adsorption 20 Before flocculating After flocculating (D[4,3]/um) Beforebetween flocculating After flocculating of CMS had occurred on Rough the surfaces of(D[4,3]/um) magnetite particles. The adsorption organic (D[4,3]/um) (D[4,3]/um) 24.3 38.37 Magnetite 12.45 22.35 Concentrate 0 polymeric flocculants and mineral particles generally depends on electrostatic attraction, Quartz 7.97 8.56 0 10 van der 0.1 Waals force 1and hydrogen bonds.100 As the magnetite particles in this dispersion condition Size/um 0.1 1 10 100 Size/um have negative surface charges, the adsorption with the negative CMS ions should not be caused by (a) (b) electrostatic attraction, but by hydrogen bonding. Since magnetite is less negatively charged than Figure 11. (a)The particle distributions of rough concentrate before andflocculation; after flocculation; (a) particle sizesize distributions of rough concentrate before and after (b) The silicaFigure (Figure11.7), theThe adsorption of CMS on magnetite by hydrogen bonding would be more favored (b) The particle size distributions of magnetite and quartz before and after flocculation. distributions of magnetite and quartz before and after flocculation. than particle that onsize silica.

Magnetite+CMS

2 1 5

6

4 3

Magnetite

4000

3500

3000

2500 2000 1500 Wavelengths/cm-1

1000

500

Figure Figure 12. 12. Infrared Infrared spectral spectral analysis. analysis.

To further understand the selective adsorption of CMS, the flocculated initial concentrate was To further understand the selective adsorption of CMS, the flocculated initial concentrate was analyzed using XPS (Thermo Electron, Waltham, MA, USA), with results shown in Figures 13 and analyzed using XPS (Thermo Electron, Waltham, MA, USA), with results shown in Figures 13 and 14, 14, and Tables 3 and 4. and Tables 3 and 4.

Counts

Table 4. Fitting results for each binding energy peak. a: Binding energy peak after flocculation; b: Binding energy peak before flocculation. C-C/C-H

Species

C-O

O=C-O Binding energy (BE) (eV) a BE (eV) b Shift (eV)

292

290

Fe

Si

Fe3 O4

SiO2

711.35 710.78 0.57

102.37 102.29 0.08

288 286 Binding energy (ev)

284

282

Figure 13. C1 XPS of the flocculated initial concentrate.

Wavelengths/cm

Figure 12. Infrared spectral analysis.

To further understand the selective adsorption of CMS, the flocculated initial concentrate was analyzed using XPS (Thermo Electron, Waltham, MA, USA), with results shown in Figures 13 and Minerals 2016, 6, 86 10 of 12 14, and Tables 3 and 4.

C-C/C-H

Counts

C-O O=C-O

292

290


284

282

Figure 13. 13. C1 XPS of the flocculated flocculated initial initial concentrate. concentrate. Figure


Fe 2p

Si 2p

Before flocculating

Counts

Counts

Before flocculating

after flocculating

716

714

10 of 12


708

706

After flocculating

105

104


(a)

101

100

(b)

Figure 14. 14. Fe Fe 2p3/2 2p3/2 and Figure andXPS XPSspectrum spectrum before before and and after after flocculation. flocculation. (a) (a) Fe Fe33OO4;4 ;(b) (b)SiO SiO2.2 .

Figure 13 and Table 3 show the fitting results for C1s binding energy spectrum. Three main Figure 13 and Table 3 show the fitting results for C1s binding energy spectrum. Three main binding energy peaks are found, which are, respectively, the C–C/C–H bond (binding energy binding energy peaks are found, which are, respectively, the C–C/C–H bond (binding energy 284.73 eV), the C–O bond (binding energy 286.54 eV), and the O=C–O bond (binding energy 284.73 eV), the C–O bond (binding energy 286.54 eV), and the O=C–O bond (binding energy 288.85 eV). 288.85 eV). These peaks are not found on pre-flocculation minerals, indicating that adsorption of These peaks are not found on pre-flocculation minerals, indicating that adsorption of CMS on CMS on concentrate particles had occurred post-flocculation [15], which is consistent with the concentrate particles had occurred post-flocculation [15], which is consistent with the results of results of infrared spectral analysis. infrared spectral analysis. Figure 14 and Table 4 show the fitting results for Fe 2p and Si 2p binding energy spectra. Figure 14 and Table 4 show the fitting results for Fe 2p and Si 2p binding energy spectra. Figure 14a Figure 14a shows the XPS-fitted peak for Fe3O4 [16]. For pre-flocculation, the binding energy of shows the XPS-fitted peak for Fe3 O4 [16]. For pre-flocculation, the binding energy of Fe 2p is 711.35 eV. Fe 2p is 711.35 eV. After-flocculation, it is 710.78 eV, which shifts 0.57 eV toward decreasing. This After-flocculation, it is 710.78 eV, which shifts 0.57 eV toward decreasing. This may be due to fact may be due to fact that the –OH and –COOH radicals of CMS, which are electronegative, have that the –OH and –COOH radicals of CMS, which are electronegative, have combined with oxygen combined with oxygen atoms on the magnetite surfaces to form hydrogen bonds (O–H...O–Fe), atoms on the magnetite surfaces to form hydrogen bonds (O–H...O–Fe), increasing the density of increasing the density of the electron cloud around Fe–O, thereby decreasing the binding energy [17]. the electron cloud around Fe–O, thereby decreasing the binding energy [17]. Figure 14b depicts the Figure 14b depicts the XPS-fitted peak for SiO2, where the binding energy of Si 2p is 102.37 eV XPS-fitted peak for SiO2 , where the binding energy of Si 2p is 102.37 eV pre-flocculation, and 102.29 eV pre-flocculation, and 102.29 eV post-flocculation. After flocculation, the binding energy of Si 2p had post-flocculation. After flocculation, the binding energy of Si 2p had shifted 0.08eV toward decrease, shifted 0.08eV toward decrease, which is less than a 0.1 eV shift, and smaller than the shift that which is less than a 0.1 eV shift, and smaller than the shift that occurred to Fe 2p. occurred to Fe 2p. Overall, the adsorption of CMS on magnetite surfaces cause magnetite particles to aggregate, Overall, the adsorption of CMS on magnetite surfaces cause magnetite particles to aggregate, increasing their sizes, largely due to the formation of hydrogen bonds between –OH and –COOH increasing their sizes, largely due to the formation of hydrogen bonds between –OH and –COOH in in CMS and oxygen atoms on particle surfaces. Under the same dispersion conditions, the negative CMS and oxygen atoms on particle surfaces. Under the same dispersion conditions, the negative surface charges of quartz particles are stronger, and the hydrogen bond-forming effect was unable to surface charges of quartz particles are stronger, and the hydrogen bond-forming effect was unable to overcome electrostatic repulsion to cause adsorption of negative CMS ions. overcome electrostatic repulsion to cause adsorption of negative CMS ions. Table 4. Fitting results for each binding energy peak. a: Binding energy peak after flocculation; b: Binding energy peak before flocculation.

Species Binding energy (BE) (eV) a

Fe Fe3O4 711.35

Si SiO2 102.37


11 of 12

4. Conclusions (1)

(2)

(3)

The tested magnetite ore from Gansu has a complex composition. It has a total iron grade of 28.36%, with magnetite as its main ferrous mineral, and quartz and feldspar as the main gangue minerals. The magnetite occurs as ultrafine particles, in dissemination or dense dissemination between gangue minerals, with relatively little singular scattered occurrence. The dissemination fineness is −0.038 mm at 90%. Through tests, we developed a multi-stage grinding-dispersion-selective flocculation-weak magnetic separation process. The optimum conditions are: 500 g/t sodium hexametaphosphate (SHMP) as dispersant, 750 g/t carboxymethyl starch (CMS) as flocculant, agitated at the speed of 400 rpm for 10 min, using slurry pH of 11, and final grinding fineness −0.03 mm at 93.45%. The tests resulted in a concentrate with iron grade 62.82%, operational recovery rate 88.31%, and total recovery rate 79.12%. Compared to simple magnetic separation, the concentrate’s iron grade had been increased by 1.26 percentage points, and the recovery rate by 5.08%. FTIR and XPS analyses show that the negative CMS ions allow selective adsorption on magnetite particle surfaces through hydrogen bonding and electrostatic forces on the surfaces, causing a significant shift of the Fe binding energy; the final particle sizes of post-flocculation concentrate had increased from 24.30 to 38.37 µm. This process has accomplished the goal of selective flocculation, and increased the separation indices.

Author Contributions: Tao Su, Tiejun Chen and Peiwei Hu had the original idea for the study. Tao Su performed the experiments and analyzed the data. Tao Su and Tiejun Chen wrote and edited the initial drafts of the manuscripts, and all authors contributed to reading and approving the final manuscript. Conflicts of Interest: The authors declare no conflict of interest.

Abbreviations The following abbreviations are used in this manuscript: SHMP SS CMS BE

Sodium Hexametaphosphate Sodium Silicate Carboxymethyl Starch Binding Energy

References 1. 2. 3. 4. 5. 6.

7. 8.

Wu, P.; Lv, X.; Qiu, J. Study on the mineral processing of a super low grade and microgranular magnetite ore. J. Mineral. Petrol. 2015, 35, 7–12. Tang, X.; Yu, Y.; Chen, W. Study on rational beneficiation technology of lean iron ore with fine disseminated minerals. Min. Metall. Eng. 2010, 1, 41–43. Su, T.; Chen, T.J.; Zhang, Y.M. The separation study on micro-fine disseminated and low-grade magnetite. Min. Res. Dev. 2015, 35, 38–42. Wei, S.; Sonsie, R.; Forbes, E.; Franks, G.V. Flocculation/flotation of hematite fines with, anionic temperature responsive polymer acting as a selective flocculant and collector. Miner. Eng. 2015, 77, 64–71. Santana, R.C.; Ribeiro, J.A.; Santos, M.A. Flotation of fine apatitic ore using micro bubbles. Sep. Purif. Technol. 2012, 98, 402–409. [CrossRef] Ravishankar, S.A.; Pradip; Khosla, N.K. Selective flocculation of iron oxide from its synthetic mixtures with cays: A comparison of polyacrylic acid and starch polymers. Int. J. Miner. Process. 1995, 43, 235–247. [CrossRef] Weissenborn, P.K.; Warren, L.J.; Dunn, J.L. Selective flocculation of ultrafine iron ore 2. Mechanism of selective flocculation. Colloids Surf. A Physicochem. Eng. Asp. 1995, 99, 29–43. [CrossRef] Abro, M.I.; Pathan, A.G.; Memon, A.R.; Sirajuddin. Dual polymer flocculation approach to overcome activation of gangue minerals during beneficiation of complex iron ore. Powder Technol. 2013, 245, 281–291. [CrossRef]


9. 10. 11. 12. 13. 14. 15.

16. 17.

12 of 12

Dogu, I.; Arol, A.I. Separation of dark-colored minerals from feldspar by selective flocculation using starch. Powder Technol. 2004, 139, 258–263. [CrossRef] Liu, C.J. Experiment study on the beneficiation of a micro-fine magnetite ore from Qinghai. Metal Mine 2009, 6, 52–55. Li, S.C.; Zhang, J.X.; Li, Z.H. Experiment study on process mineralogy and beneficiation of micro-fine magnetite ore from Liaoning. Min. Metall. Eng. 2012, 32, 312–315. Arol, A.I.; Aydogan, A. Recovery enhancement of magnetite fines in magnetic separation. Colloids Surf. A Physicochem. Eng. Asp. 2004, 232, 151–154. [CrossRef] Huang, Y.; Han, G.; Liu, J.; Wang, W. A facile disposal of Bayer red mud based on selective flocculation desliming with organic humics. J. Hazard. Mater. 2016, 301, 46–55. [CrossRef] [PubMed] Hui, R.H.; Guan, C.X.; Hou, D.Y. Study on IR characteristics of carboxylic acid and their salts. J. Anshan Teach. Coll. 2001, 3, 95–98. Mikhlin, Y.; Karacharov, A.; Tomashevich, Y. Cryogenic XPS study of fast-frozen sulfide minerals: Flotation-related adsorption of N-butyl xanthate and beyond. J. Electron Spectrosc. Relat. Phenom. 2016, 206, 65–73. [CrossRef] Cai, Y.; Pan, Y.; Xue, J. Comparative XPS study between experimentally and naturally weathered pyrites. Appl. Surf. Sci. 2009, 255, 8750–8760. [CrossRef] Li, S.; Wang, B.; Feng, W. Synchrotron radiation photoelectron spectroscopy study of dextrant-coated Fe3 O4 magnetic nanoparticles. Nucl. Technol. 2009, 32, 251–255. © 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).