New Technologies for HCl Regeneration in Chloride

George P. Demopoulos et al.: New Technologies for HCl Regeneration in Chloride Hydrometallurgy

New Technologies for HCl Regeneration in Chloride Hydrometallurgy George P. Demopoulos, Zhibao Li, Levente Becze, Georgiana Moldoveanu, Terry C. Cheng, Bryn Harris

Chloride-based aqueous leaching processes find increasingly new applications in the area of metal recovery from primary (ores or concentrates) or secondary (such as slags or dusts) raw materials. A critical operation in all these processes is the regeneration of the lixiviant, namely hydrochloric acid. Pyrohydrolysis is the commercial technology of choice when it comes to HCl regeneration. However, the high capital and energy costs associated with the installation and operation of pyrohydrolysers prove prohibitive in many new mineral/metal processing projects, hence development of low-cost alternative options is highly desirable. It is the scope of this paper to review and discuss some new HCl regeneration process concepts that are currently attracting considerable R&D attention. The new process options considered are:

1. HCl regeneration via metal sulphate salt crystallization; 2. HCl regeneration via “hydrolytic distillation”. Examples of the first process option are the crystallization of calcium, magnesium and ferrous sulphate salts by reaction of spent metal chloride solutions with H2SO4. Process option 2 involving HCl vapour distillation under evaporative hydrolysis conditions (at T > 120 °C) can be applied to FeCl2/FeCl3 solutions. It is the object of this paper to describe and discuss these new process developments with the aid of laboratory-scale data, thermodynamic calculations and relevant flowsheets. Keywords: Chloride hydrometallurgy – Leaching process – Metal recovery – Regeneration of acid

Neue Technologien für die HCl-Regeneration in der chloridischen Hydrometallurgie In zunehmendem Ausmaß bedient man sich neuer Anwendungen wässriger Laugungsprozesse auf Chlorbasis auf dem Gebiet des Metallausbringens aus primären (Erze oder Konzentrate) wie auch sekundären (Schlacken oder Stäube) Rohstoffen. Ein kritischer Arbeitsgang in all diesen Verfahren ist die Regeneration des Laugungsmittels, nämlich der Salzsäure. Wenn es um die HCl-Regeneration geht, ist die Pyrohydrolyse die industrielle Methode der Wahl. Die hohen Kapital- und Energiekosten für Bau und Betrieb von Pyrohydrolyseanlagen erwiesen sich jedoch als prohibitiv für viele neue Erz/Metallverarbeitungsprojekte. Deshalb ist die Entwicklung neuer, preisgünstiger alternativer Optionen höchst wünschenswert. In diesem Artikel sollen neue HCl-Regenerationsverfahrenskonzepte vorgestellt und diskutiert werden, die derzeit in Forschung und Entwicklung erhebliche Aufmerksamkeit erregen. Die betrachteten neuen Verfahrenskonzepte sind:

1. HCl-Regeneration über Metallsulfatsalz-Kristallisation, 2. HCl-Regeneration durch „hydrolytische Destillation“. Beispiele für die erstgenannte Verfahrensoption sind die Kristallisation von Calcium-, Magnesium- und Ferrosulfatsalzen durch Reaktion von verbrauchten Metallchloridlösungen mit H2SO4. Die zweite Verfahrensoption beinhaltet HCl-Dampfdestillation unter hydrolytischen Verdampfungsbedingungen (bei T > 120 °C) und kann für FeCl2/Fe-Cl3-Lösungen angewandt werden. Zweck dieses Artikels ist die Beschreibung und Erörterung dieser neuen Verfahrensentwicklungen mit Hilfe von Labordaten, thermodynamischen Berechnungen und relevanten Fließbildern. Schlüsselwörter: Chlorid-Hydrometallurgie – Laugungsverfahren – Metall ausbringen – Säureregeneration

Nouvelles technologies pour la régénération du HCl dans la métallurgie chloridique Nuevas tecnologías para la regeneración de HCl en la hidrometalurgia del cloruro Paper presented on the occasion of the European Metallurgical Conference EMC 2007, June 11 to 14, 2007, in Düsseldorf. World of Metallurgy – ERZMETALL 61 (2008) No. 2

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1

Introduction

The use of high concentration chloride solutions (brines) in hydrometallurgy as opposed to sulphate solutions (with or without the addition of small chloride addition as catalyst) holds a lot of promise if a low cost HCl regeneration process becomes available. This is due particularly to the unique chemistry of these solutions that allows refractory and complex sulphidic or oxidic mineral feedstocks to be processed without resorting to capital-intensive autoclave technology. Improved metal separations in chloride solutions including recovery of precious metals is another advantage. The reader is referred to relevant technical review articles for discussion of the chemistry of chloride hydrometallurgical solutions and processes [1-5]. Examples of leaching processes making use of concentrated chloride media are: The upgrade of molybdenum concentrate by leaching copper and lead in CaCl2-FeCl3 solutions at 110 °C in the 70s [6]; the UGS process commercialized by QIT – a Rio Tinto Iron & Titanium company – to upgrade its TiO2containing slag material to synthetic rutile feedstock [7]; the atmospheric leaching of zinc sulphide concentrates with HCl-O2 [8] or HCl-ZnCl2 systems [9]; the HCl leaching of laterite ores in MgCl2 [9, 10] or CaCl2 brine solutions [11]; and finally the leaching of chalcopyrite concentrates in concentrated chloride solutions (> 4M Cl-) with chlorine [12-14], or hydrochloric acid [15, 16]. In oxidative chloride leaching systems, the regeneration of the lixiviant, typically CuCl2/FeCl3 or Cl2, is linked to metal recovery by electrowinning, as done for example in the nickel industry [17] and extended recently by Sumitomo to copper concentrate treatment [14]. An interesting recent development is the use of chlor-alkali technology in Outokumpu’s HydroCopper Process to separate metal recovery from chlorine production. In this case, the NaCl electrolyte is split into Cl2 and H2 with concomitant caustic generation. Chlorine is used to regenerate CuCl2 and FeCl3 in the leaching circuit, while H2 is used for the reduction of the intermediate Cu2O product to copper metal [12-13]. When it comes to acid leaching systems requiring regeneration of HCl, the technology of preference is pyrohydrolysis [18]. This technology is well established in the steel industry where it is used for production of HCl from iron chloride liquors [19]. Although not driven from an acid regeneration point of view, the technology has also found application in the production of nickel oxide from NiCl2 solutions [20]. A recent innovative application of pyrohydrolysis for the purpose of recovering acid from waste multi-component metal chloride solutions consisting of MgCl2–FeCl2–FeCl3–AlCl3 is noteworthy [7, 21]. Pyrohydrolysis, despite its effectiveness and proven record, remains, however, a highly capital- and energy-intensive technology that makes it in many cases not an economically viable option. This is for example the case of MgCl2 pyrohydrolysis proposed previously for acid regeneration in connection to the HCl-O2 leaching of complex zinc sulphide concentrates [8] or the leaching of laterites in HCl-MgCl2 media [22]. Hence, the search for low cost HCl regeneration alternatives to pyrohydrolysis has attracted a lot of attention recently. 90

One of the options that was proposed by Van Weert and Peek in 1992 [17] and investigated by Liao [23] involves a hydrogen diffusion anode in an electrowinning cell equipped with membrane for the generation of HCl instead of chlorine. Membrane stability and avoidance of parasitic chlorine generation in a rather complex cell design seem to have hampered the further development of this option. Another option investigated at McGill over the past five years [24, 25] is based on the reaction of H2SO4 with spent CaCl2 leach solution to crystallize calcium sulphate with concomitant production of azeotropic HCl strength acid. This reaction forms part of the Intec laterite leaching process [11]. A similar concept is advocated by Anglo Operations [9] and Eco-Tec [26] for the regeneration of HCl by crystallization of metal sulphate salts like those of zinc, magnesium, or ferrous iron from the respective spent acid metal chloride solutions with the addition of sulphuric acid. HCl regeneration via the crystallization of metal sulphate salts constitutes the first option discussed in detail in this paper. The second option discussed is based on the concept of hydrolysis (that of iron in particular), but in this case HCl is recovered in the vapour phase via distillation at the boiling point of the brine solution. Process flowsheets incorporating the latter technology concept are currently being developed and tested at the pilot stage for the treatment of a complex copper-nickel sulphide ore in Canada [15, 16] and the atmospheric chloride leaching of lateritic ore in Australia [10].

2

Concentrated HCl-metal chloride solutions as leaching media

It is now well known that the activity of HCl, or more accurately the activity of the proton, increases multifold in the presence of metal chloride salts, thus rendering HCl-metal chloride solutions highly effective leaching media under atmospheric pressure conditions [27-29]. The chlorides of sodium, calcium, and magnesium already have been used or proposed to enhance the leaching power of HCl [1-6]. But what is less known is that FeCl2 – a common component in chloride hydrometallurgical or pickle liquors – can be equally used to enhance the activity of hydrochloric acid. This is exemplified with the proton activity data presented in Figures 1 and 2 as a function of metal chloride concentration and temperature, and has been confirmed in laboratory testing on the Starfield Project referred to above. These data were generated with the aid of OLI Systems’ Stream Analyzer software package [30]. As it can be seen, the hydrogen ion activity increases with increasing metal chloride concentration well above the nominal HCl concentration, with the divalent chlorides being more effective than NaCl. This is true independent of HCl concentration and temperature. There seems to be no difference among the divalent metal chlorides when it comes to increasing the acid activity, meaning that, in theory, they are equally effective as leaching media. However, except for MgCl2, the other metal chlorides exhibit a decrease in solubility with increasing HCl concentration or decreasing temperature (refer to Figure 2 (top)) and this has to be taken into account when a process is designed. Thus, for example, World of Metallurgy – ERZMETALL 61 (2008) No. 2

George P. Demopoulos et al.: New Technologies for HCl Regeneration in Chloride Hydrometallurgy 60.000

3.000 0.5m 0.5m 0.5m 0.5m

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Fig. 1: Calculated values of aH+ in 0.5 m HCl + NaCl, MgCl2, FeCl2, or CaCl2 solutions at 25 °C (top) and 100 °C (bottom)

Fig. 2: Calculated values of aH+ in 4 m HCl + NaCl, MgCl2, FeCl2, or CaCl2 solutions at 25 °C (top) and 100 °C (bottom)

problems may be experienced during solid-liquid separation as a result of crystallization of part of the salt upon cooling of the solution. This is particularly true in the case of NaCl. Similarly, the interactive effect among metal chlorides on their solubility needs to be taken into account. It is interesting to note in this context that the presence of MgCl2 causes the solubility of other divalent metal chlorides, like FeCl2 to decrease due to its high hydration affinity that leads to loss of water activity and solvency. Other issues such as the effect of the metal chloride on the dissolution of magnesium from laterite feedstocks as described by Harris et al. [31] may influence the ultimate choice of lixiviant system. In conclusion, whilst leaching simply with hydrochloric acid, as tested for example by Gibson and Rice [32] in the case of laterites, is technically effective, the enhanced activity of the proton in concentrated divalent metal chloride systems is a very real phenomenon, leading to considerably less acid consumption (virtually stoichiometric), and more importantly, appreciably enhanced kinetics and total metal recovery [10]. Recovery of HCl from such solutions is discussed in the following sections of the paper.

least 6 M) spent leach solutions to crystallize the equivalent metal sulphate salt (which in general is significantly less soluble than its chloride counterpart) and simultaneously produce high strength hydrochloric acid solution suitable for recycling to the leaching circuit of the process.

3

HCl regeneration via metal sulphate crystallization

In this system, sulphuric acid is added to high concentration metal chloride (with total chloride concentration at World of Metallurgy – ERZMETALL 61 (2008) No. 2

3.1

Calcium sulphate crystallization

An example of a chloride hydrometallurgical process where HCl regeneration via calcium sulphate crystallization may be applied is presented in Figure 3. The original patented process involves the leaching of zinc sulphide material using HCl and O2 followed by precipitation of zinc oxide using magnesium oxide (MgO) as a neutralizing agent. This results in the production of a spent MgCl2 solution which is subsequently pyrohydrolyzed to regenerate HCl so that the latter can be recycled to the leaching step [8]. A prefeasibility study concluded that the process is not economically viable due primarily to the high capital and operating costs associated with pyrohydrolysis. As a low cost alternative, the use of lime (CaO) followed by reaction of the resultant spent CaCl2 leach solution with sulphuric acid (H2SO4) to regenerate HCl was investigated. Production of saleable quality gypsum, or even better, the high value α-CaSO4 hemihydrate was set as the goal [25]: CaCl2 + H2SO4 + n H2O → CaSO4⋅nH2O(s) + 2 HCl(aq) (1) 91


Leaching

Regenerated HCl

O2

Fig. 3: Example of a chloride hydrometallurgical process incorporating HCl regeneration with two alternative processes: pyrohydrolysis of MgCl2 and reactive crystallization of gypsum (reproduced from [24])

Precipitation

CaO

ZnO Product

S L MgCl2 Pyrohydrolysis

In summary, here are the salient features of the developed HCl regeneration process via the crystallization of saleable calcium sulphate materials by reaction of calcium chloride solution with sulphuric acid. 1) Reactive crystallization can either be performed to produce common gypsum (CaSO4⋅2H2O) or the alpha high value variety (CaSO4⋅½H2O) depending on the applied temperature and conditions. Typically gypsum is produced at T ≤ 60 °C while α-hemihydrate requires 70 to 90 °C. Crystallization outside an established (T– HCl–CaCl2–Time) operating window leads to the production of the undesirable anhydrite (CaSO4) variety. A conceptual flowsheet variant designed for the production of α-gypsum is illustrated in Figure 4. 2) For the production of azeotropic strength acid, a 3-4 M CaCl2 concentration is required, hence the spent leach solution is passed through an evaporation1 section (I) with the produced condensate used for the washing of the product cake (section V). At the same time, the H2SO4 concentration of the limiting reactant needs to be adjusted by dilution from the typical 96 % down to It is clarified here that this pre-concentration step is a standard feature also of all pyrohydrolysis processes [19, 35]. However, in the latter case the pre-concentrated liquor is completely evaporated in the pyrohydrolyser hence its higher energy demand vis-à-vis the crystallization alternative process discussed here.

92

ZnCl2

MgO

Such a reaction can take place readily and under atmospheric pressure, but without proper design and control may lead to gel-like precipitate formation rendering the process not operational, hence the solution [30, 33] and crystallization [24, 25] chemistry of the CaCl2–H2SO4–MeClx–H2O system was extensively studied. As a result of this research work, a conceptual flowsheet was designed and subjected to mass/energy calculations and validation via small laboratory tests, while a plant design exercise was undertaken by an external group [34].

1

Leach residue

S L

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Regenerated HCl

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~50 % (stream 4) before being added to the crystallization reactors (section II). This is done with the aid of the generated filter cake wash water (stream 10). 3) The molar ratio of SO4/Ca should be kept below 1 (preferably at ~0.8) so that a small fraction of CaCl2 remains in solution in order to lower the soluble fraction of CaSO4 on the one hand [30], and on the other to enhance the stability of α-hemihydrate gypsum [25]. 4) The crystallization (reaction) kinetics should be regulated under a low supersaturation environment by stagewise addition of H2SO4 to avoid gel-like formation of the calcium sulphate precipitate. Typically, four or more crystallization reactors (section 2) of one hour residence time each are required. To promote the heterogeneous nucleation and crystal growth that is necessary for the Spent CaCl2 solution (1) H2O (2)

Evaporation (I) (3)

Crystallization (II)

(4)

H2SO4

(5)

Cooling (III) (7)

Filtration (IV)

(8) Regenerated HCl sent to leaching

(9) Wash water

(6)

Cake washing (V)

(10) to H SO 2 4 make-up

(11)

CaSO4 · ½ H2O(s) Fig. 4: HCl regeneration via the reaction of CaCl2 with H2SO4

World of Metallurgy – ERZMETALL 61 (2008) No. 2

George P. Demopoulos et al.: New Technologies for HCl Regeneration in Chloride Hydrometallurgy production of clean and easily filterable gypsum crystal materials, part of the filter cake product is recycled to serve as seed. As a result of this process feature, excellent filtration rates in the order of ~4000 kg dry solids/ (m2/h) are consistently obtained with crystals having average size > 50 µm. In terms of purity, the crystals typically contain less than 0.1% chloride and negligible ( 99 % recovery. Good quality hematite is produced. This reaction scheme has been confirmed in the laboratory at McGill and has now been extended to the case of solutions with a magnesium chloride matrix.

2m MgCl2 3m MgCl2 4m MgCl2

HCl in solution [m] Fig. 8: HCl Vapour-liquid equilibria for the HCl–MgCl2–H2O system at boiling point

ing operation. In another configuration [16], hydrolytic distillation was successfully carried out by adding in a semi-continuous mode MgCl2-FeCl3 solution to magnesium chloride solution heated over a period of three hours up to 250 °C. Once more, azeotropic strength acid was obtained. Further work is currently underway aiming to arrive at an optimum reactor/process design and pilot-plant scale testing. In Figure 9, the integration of the hydrolytic distillation unit operation to a new leaching process currently under development for the treatment of the Ferguson Lake massive Cu-Ni sulphide ore deposit located in Northern Canada is illustrated [15, 16]. The whole ore rather than a concentrate is leached in recycled magnesium chloride and hydrochloric acid at 105 °C – the boiling point of the brine solution is 117 °C. With the exception of the bulk of the pyrite the other iron sulphide minerals react with HCl producing hydrogen sulphide gas, which has the advantage of removing most of the sulphide sulphur directly from the solids and the circuit at the outset, and leaving an upgraded base and precious metals concentrate. The gas can be burnt or treated in a Claus Reactor, either of which recovers a considerable amount of the intrinsic energy contained in the ore. The magnesium chloride/ferrous chloride leach liquor is oxidised very efficiently by oxygen as reported previously [31] to form FeCl3 of which part is employed

Fig. 9: Proposed HCl-MgCl2 leaching circuit for the treatment of the Starfield massive sulphide ore incorporating lixiviant regeneration by hydrolytic distillation (reproduced from [16])


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George P. Demopoulos et al.: New Technologies for HCl Regeneration in Chloride Hydrometallurgy as the lixiviant in the second stage leach, and the balance is processed in the hydrolytic distillation unit. The oxidation of ferrous chloride, which is controlled by oxygen mass transfer, is associated with partial precipitation of iron in the form of hematite (refer to Reaction (2)) under the applied conditions: 120 to 150 °C. The balance of iron precipitates in the hydrolytic distillation unit (operating in the T range: 200 to 250 °C), where HCl is recovered and returned to the primary leach stage upon recombining with the spent MgCl2 solution. 4.3

The FeCl2-HCl lixiviant system

The proton activity data presented in section 2 showed that FeCl2 is equally effective as the common divalent metal chlorides of magnesium and calcium in enhancing the leaching power of HCl. This means that theoretically FeCl2 can replace MgCl2 or CaCl2 to make up the HClSalt lixiviant in the case of processing of some sulphidic feedstocks. This can prove beneficial, when it comes to HCl regeneration since as per the PORI process (refer to section 4.1) hydrolytic distillation can be run at 180 °C instead of the higher temperatures required in the MgCl2 system (200 to 250 °C) with the added advantage of recovery of super-azeotropic acid (30 %) [37]. A simple flowsheet demonstrating this process option is presented in Figure 10. The leaching of a sulphidic ore in FeCl2 (4 M)-HCl lixiviant solution is considered2. Following solid/liquid separation, the generated FeCl2 leach solution is split with the bulk of it going to metal recovery (if applicable – see footnote) while the rest is sent to the iron precipitation-lixiviant regeneration section. The latter consists of two steps: (a) oxidation corresponding to Reaction (2) and (b) hydrolytic distilThis non-oxidative leaching system has proven effective, for example, in dissolving the pyrrhotite component of a massive Cu-Ni sulphide ore resulting in a 5-10fold value metal enrichment [15]. The enriched material can be subsequently subjected to a secondary oxidative leach to effect value metal recovery as done in the Starfield process [16] or sent to a smelter depending on its leaching response and specific site conditions. 2

lation corresponding to Reaction (3). During oxidation, which occurs readily at 130 to 150 °C, 1/3 of the ferrous iron precipitates as hematite while the remaining converts to ferric chloride. The latter is fed to the hydrolytic distillation step operating at 180 °C where HCl volatilization occurs under simultaneous hematite precipitation. The produced super-azeotropic acid is recycled back to the leaching operation after combining with the returning spent FeCl2 solution. It has to be clarified here that only the iron leached from the ore (typically its reactive pyrrhotite content) is subjected to oxidation and hydrolysis with the background (typically 4 M) FeCl2 simply being recirculated as done with the MgCl2 circuit (see Figure 9). For example the processing of a sulphidic ore with 46 % iron content (as FeS) in HCl-FeCl2 (4 M) lixiviant solution requires theoretically only 12 % of the solution to be subjected to oxidation-hydrolytic distillation.

5

Conclusion

According to recent R&D work done at McGill University and elsewhere, hydrochloric acid may be regenerated and reused as a lixiviant out of spent concentrated (at least 6 M total chloride content) metal chloride solutions without resorting to energy-intensive pyrohydrolysis technology. This can be done, in particular, by two process options considered in this paper. The first one involves the use of sulphuric acid and crystallization of metal sulphate salts with simultaneous regeneration of HCl, while the second one employs the hydrolytic precipitation of iron as hematite accompanied by volatilization of HCl under controlled evaporation at temperatures as high as 250 °C. The crystallization approach has been studied in detail for the case of HCl regeneration from spent CaCl2 solutions as per the reaction below: CaCl2(3-4M) + H2SO4(5-8M) + nH2O → CaSO4⋅nH2O(s) + 2HCl(aq)(~6 M)

(4)

The reaction may be controlled to yield calcium sulphate dihydrate (gypsum) or the higher value α-calcium sul-

Fig. 10: Conceptual flowsheet of an HClFeCl2 lixiviant process incorporating non-oxidative leaching of a sulphidic ore and HCl regeneration via hydrolytic distillation

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George P. Demopoulos et al.: New Technologies for HCl Regeneration in Chloride Hydrometallurgy phate hemihydrate. Typically, the first product is obtained at 60 °C or lower temperatures, while the second one in the 70 to 90 °C temperature range. Multi-stage crystallization in a series of CSTR-type crystallizers and crystal recycling is required to yield impurity-free and easily filterable products. Small-scale test and mass balance calculations have confirmed the technical feasibility of producing azeotropic-strength HCl via this route. An independent cost-estimation study found the crystallization-based regeneration process to be at least 30 % less costly, both in terms of capital and of operating expenses, when compared to pyrohydrolysis, even when no value is assigned to the calcium sulphate products. As per solubility calculations, it is, in principle, feasible to regenerate HCl by crystallization of other salts such as magnesium sulphate for the treatment of laterite ores, or ferrous sulphate for the treatment of pickle liquors. The hydrolytic precipitation-HCl volatilization route was originally developed in the early 70s as the PORI Process for the treatment of pickle liquors, which are essentially pure ferrous chloride solutions. However, recent R&D work has extended this process concept to magnesium chloride-based leaching media which are considered for either the treatment of Cu-Ni massive sulphide ore or laterite ores. The process involves two steps: (a) Oxidation of FeCl2 with O2 at ~135 to 150 °C as per Reaction (5) below, and (b) hydrolytic distillation of FeCl3 as per Reaction (6): 12FeCl2(aq) + 3O2(g) → 2Fe2O3(s) + 8FeCl3(aq)

(5)

2FeCl3(aq) + 3H2O(g,aq) → Fe2O3(s) + 6HCl(g,aq)

(6)

In the case of FeCl3 alone (i.e. with no other chloride salts present), Reaction (6) – dubbed “hydrolytic distillation” – proceeds to completion at ~175 °C, while higher temperatures (up to 250 °C) are required when MgCl2 is present. The process does not involve autoclaves, but rather the boiling of the brine solution under atmospheric pressure to drive-off and collect HCl in the vapour phase. The volatilization of HCl drives Reaction (6) to completion. The process leads to production of azeotropic (or higher concentration) HCl acid that can be conveniently recycled to the leaching operation. It has also been determined that under certain conditions, FeCl2-HCl can be used as lixiviant for sulphidic ores rich in pyrrhotite allowing for easier HCl regeneration. Intensification of R&D efforts in further developing these low temperature alternatives to pyrohydrolysis is expected to lead to viable new chloride hydrometallurgical technology for the processing of a variety of primary and/or secondary feed materials, as they currently are the Starfield (sulphide leaching) and Jervois (laterite leaching) projects.

as is Hans Volstad of Hatch for his flowsheet design contributions. Finally, the valuable work of former students Ms. Amani Al-Othman and Dr. Seref Girgin (gypsum crystallization) and fellow hydrometallurgist Carl White (hydrolytic distillation) is greatly acknowledged.

References [1] Dutrizac, J.E. (1992): The leaching of sulphide minerals in chloride media. – Hydrometallurgy, 29: 1-45. [2] Aprahamian, V.H. & Demopoulos, G.P. (1995): The solution chemistry and solvent extraction behaviour of Cu, Fe, Ni, Zn, Pb, Sn, Ag, As, Sb, Bi, Se and Te in acid chloride solutions reviewed from the standpoint of PGM refining. – Mineral Processing and Extractive Metallurgy Review, 14: 143-167. [3] Senanayake, G. & Muir, D.M. (2003): Chloride processing of metal sulphides: review of fundamentals and applications. – Proceedings of the 5th International Symposium Hydrometallurgy 2003, August 24-27, Vancouver, Canada: pp. 517-531. TMS, Warrendale, PA, USA. [4] Dreisinger, D. (2004): New developments in hydrometallurgical treatment of copper concentrates. – Hydro-Sulfides 2004, International Colloquium on Hydrometallurgical Processing of Copper Sulfides, 2004: pp. 47-74. Universidad de Chile, Santiago, Chile. [5] Harris, B. et al. (2004): Atmospheric chloride etc leaching of base metal sulphides. – Proceedings of Hydro-Sulfides 2004, International Colloquium on Hydrometallurgical Processing of Copper Sulfides: pp. 384-398. Universidad de Chile, Santiago, Chile. [6] Jennings, P.H., Stanley, R.W. & Ames, H.L. (1973): Development of a process for purifying molybdenite concentrates. Proceedings of Second International Symposium on Hydrometallurgy: p. 868. New York (AIME). [7] Borowiec, K. Grau, A.E., Gueguin, M., Turgeon, J.-F. (1998): Method to upgrade titania slag and resulting product. US Patent, No. 5,380,420, Nov. 3, 1998. [8] Allen, C., Kondos, P., Payant, S., Van Weert, G., Van Sandwijk, A. (2002): Production of zinc oxide from complex sulphide concentrates using chloride processing. US Patent No. 6,395,242, May 28, 2002. [9] Smit, J.T., Steyl, J.D.T. (2006): Leaching process in the presence of hydrochloric acid for the recovery of a value metal from an ore. International Patent, PCT, WO 2006/043158, April 27, 2006. [10] Harris, B. et al. (2006): A New approach to the high concentration chloride leaching of nickel laterites. Presented at ALTA Nickel/Cobalt 11, Perth, Australia 2006. [11] Moyes,A.J. (2005):The Intec Nickel Laterite Process. Presented at ALTA 2005 Ni/Co 10, Perth, Australia.

Acknowledgments

[12] Hyvärinen, O., Hämäläinen, M. & Leimala, R. (2002): Outokumpu HydroCopper™ Process – A novel concept in copper production. – Proceedings of the 32nd Annual Meeting – Chloride Metallurgy 2002 – of the Hydrometallurgy Division of the Canadian Institute of Mining, Metallurgy, and Petroleum held in Montreal, October 2002: Vol. 2, pp. 609-613. Montreal, Canada (CIM).

NSERC (The Natural Sciences and Engineering Research Council of Canada), Starfield Resources Inc. and Hatch are thanked for supporting parts of this work. In addition Peter Kondos and Gus van Weert are thanked for their early involvement with the gypsum crystallization system,

[13] Haavanlammi, L., Hyvärinen, O. & Karonen, J. (2006): Iron behaviour in the HydroCopper™ Process. – Proceedings of the Third International Symposium on Iron Control in Hydrometallurgy held in Montreal, October 1 to 4, 2006: pp. 221-230. Montreal, Canada (CIM).


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George P. Demopoulos et al.: New Technologies for HCl Regeneration in Chloride Hydrometallurgy [14] Imamura, M. et al. (2006): Iron recovery in the Sumitomo Chlorine Leach Process for copper concentrates. Proceedings of the Third International Symposium on Iron Control in Hydrometallurgy held in Montreal, October 1 to 4, 2006: pp. 191-204. Montreal, Canada (CIM). [15] Harris, B., White, C., Ballantyne, B. (2006): Chloride leaching of polymetallic massive sulphide. Presented at ALTA Copper 10, Perth, Australia. [16] Harris, G.B. et al. (2007): Recovery of copper from a massive polymetallic sulphide by high concentration chloride leaching. – Proceedings of the Conference Copper – Cobre 2007, Hydrometallurgy of Copper, held in Toronto/Canada, August 2007. Montreal, Canada (CIM). [17] Van Weert, G. & Peek, E.M.I. (1992): Reagent recovery in chloride hydrometallurgy-some missing links. – Hydrometallurgy, 29: 513-526. [18] Steinbach, W. & Baerhold, F. (2002): Comparison of spray roasting and fluidized bed granulation for recovery of hydrochloric acid fro metallurgical processes though pyrohydrolysis. Proceedings of the 32nd Annual Meeting – Chloride Metallurgy 2002 – of the Hydrometallurgy Division of the Canadian Institute of Mining, Metallurgy, and Petroleum held in Montreal, October 2002: pp. 643-655. Montreal, Canada (CIM). [19] Baerhold, F., Lebl, A. & Statrcevic, J.(2006): Recycling of spent acids and iron via pyrohydrolysis. Proceedings of the Third International Symposium on Iron Control in Hydrometallurgy held in Montreal, October 1 to 4, 2006: pp. 789-803. Montreal, Canada (CIM). [20] Vahed, A. et al. (2004): Development of a fluid bed pyrohydrolysis process for Inco’s Goro Nickel Project. – Proceedings of International Laterite Nickel Symposium 2004 held in Charlotte, USA, March 14-18, 2004: pp. 171-191. Warrendale, USA (TMS). [21] Patoine, M.-C. et al. (2002): Pyrohydrolysis of a calcium and magnesium bearing FeCl2 leach liquor. Proceedings of the 32nd Annual Meeting – Chloride Metallurgy 2002 – of the Hydrometallurgy Division of the Canadian Institute of Mining, Metallurgy, and Petroleum held in Montreal, October 2002: pp. 699-712. Montreal, Canada (CIM). [22] Harris, G.B. et al. (2004): The Jaguar Nickel Inc. Sechol Laterite Project Atmospheric Chloride Leach Process. – Proceedings of International Laterite Nickel Symposium 2004 held in Charlotte, USA, March 14-18, 2004: p. 219. Warrendale, USA (TMS).

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[23] Liao, L.Z. (1997): The application of ion exchange membranes in chloride related electrochemical technology. Ph.D. Thesis, Delft University of Technology, Delft, Netherlands. [24] Al-Othman, A., Cheng, T.C. & Demopoulos, G.P. (2004): Regeneration of HCl and production of saleable gypsum by reaction of spent CaCl2 leach solutions with H2SO4. Proceedings of the 5th International Symposium on Waste Processing and Recycling in the Mineral and Metallurgical Industries held in Hamilton, Ontario, Canada, August 22 to 25, 2004: pp. 453-467. Montreal, Canada (CIM) [25] Girgin, S. & Demopoulos, G.P. (2004): Production of the high value material, alpha-CaSO4 hemihydrate out of spent CaCl2 solutions by reaction with H2SO4. EPD Congress 2004: pp. 627-639. Warrendale, USA (TMS). [26] Brown, C.J. & Olsen, D.R.: Regeneration of hydrochloric acid pickle liquors by crystallization. Proceedings of the Third International Symposium on Iron Control in Hydrometallurgy held in Montreal, October 1 to 4, 2006: pp. 831-843. Montreal, Canada (CIM).

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Prof. Dr. George P. Demopoulos Dr. Zhibao Li Dr. Levente Becze Dr. Georgiana Moldoveanu Dr. Terry C. Cheng Dr. Bryn Harris All: McGill University Department of Mining, Metals and Materials Engineering 3610 University Street H3A 2B2 Montreal, Quebec Canada
