Environmental Engineering and Management Journal
November/December 2009, Vol. 8, No.6, 1413-1419
http://omicron.ch.tuiasi.ro/EEMJ/
“Gheorghe Asachi” Technical University of Iasi, Romania
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Modeling, Simulation and Optimization OPTIMIZATION OF PROCESS VARIABLES TO MAXIMIZE THE COPPER LOADING CAPACITY OF PUROLITE S930 RESIN Petru Bulai∗, Catalin Balan, Corneliu Cojocaru, Matei Macoveanu “Gh. Asachi” Technical University of Iasi, Faculty of Chemical Engineering & Environmental Protection, Department of Environmental Engineering & Management, 71 A, D. Mangeron Blvd., 700050 Iasi, Romania
Abstract The practical capacity of an ion exchange or chelating resin depends on various process variables, such as initial solution pH, initial metal ion concentration, metal/resin ratio, contact time and temperature. This work presents the optimization of process variables to maximize the copper loading capacity of chelating resin Purolite S930. To study the combined effect of the initial solution pH, initial Cu (II) concentration and resin dosage were used a 23 orthogonal central composite design for experiments design and Response Surface Methodology (RSM) for analysis of experimental results. The Gradient method was used to optimize the regression equation. The optimum values of these variables were found to be pH = 4.77, C = 246.60 mg Cu/L and a = 0.394 g resin/L, respectively; in this point loading capacity is the maximum one (146.641 mg Cu(II)/g given by empirical model and 144.22 confirmed experimentally).
Key words: Copper (II) removal, Gradient method, Optimization, Purolite S 930, RSM 1. Introduction Copper is one of heavy metals with a great solubility in aquatic medium and, at excessive levels, has hazardous effects to many life forms. Introduced into the surface waters copper is highly phytotoxic and influence the production rate and diversity of planktonic species (Passos et al., 2006). Copper concentration into environmental it doesn’t reduce by any biological, chemical or photo self-purification processes. Due to its bioaccumulation tendency and persistence in nature, copper is accumulating in the food chain and aquatics sediments. The main sources of wastewater containing copper are metal cleaning and plating baths, battery production, iron and steel production, refineries, paper and pulp, wood preservatives, fertilizer and agricultural operations (Bulai et al., 2009; Khazali et al., 2007; Veli and Alyüz, 2007). The limits of Cu (II) into wastewater are 0.25 mg/L according EPA regulations (Selvaraj et al., 2007) and 0.1mg/L according to Romanian regulation (NTPA001/2005). The most important techniques for ∗
copper removal from wastewater are chemical precipitation (Soylak and Erdogan, 2006), coagulation–flocculation, flotation (Polat and Erdogan, 2007), membrane filtration: ultrafiltration, nanofiltration (Ahmad and Ooi, 2006) and reverse osmosis; electrochemical treatment techniques: electro dialysis, membrane electrolysis and electrochemical precipitation, electroextraction (Smara et al., 2005; Stephenson and Dryfe, 2007); sorption treatment techniques: ion exchange (Demirbas et al., 2005; Pohl and Prusisz, 2004), adsorption (Weng et al., 2007; Passos et al., 2006; Veli and Alyuz, 2007), biosorption (Cojocaru et al.., 2009; Dunda et al., 2007; Ho et al., 2002; Singh et al., 2007; Tuzen et al., 2007). Application of the ion exchange process in copper removal from wastewater has a positive ecological effect because the treated water can be recycled in process. Moreover, copper can be concentrated in different combinations using inorganic acid (HCl, H2SO4), salts or EDTA and reused in the same process or a different one. The influence of solution pH, initial metal concentration, contact time, temperature, ionic form of the resin and
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Bulai et al./Environmental Engineering and Management Journal 8 (2009), 6, 1413-1419
resin dose on the practical ion exchange capacity (loading) is mostly studied in batch experiments. However, for an optimal use of the resin is important to known the initial process parameters at which the resin has the great capacity. The purpose of this work was to maximize the copper loading capacity of Purolite S930 chelating resin by optimization of the combined effect of the initial solution pH, initial Cu (II) concentration and resin dose.
solution was determined by spectrophotometric method with rubeanic acid (λ = 395 nm, linear range 1-4 mg Cu / L) (Popa and Moldoveanu, 1969) using a Hach DR/2000 spectrophotometer. For sorption kinetics experiments, the procedures were the same as those presented in equilibrium and modeling experiments but the samples were analyzed after a specified period of contact time. The sorption of Cu (II) by Purolite S930-H resin was quantitatively evaluated by amount of Cu (II) retained on resin, Q (mg/g):
2. Experimental Q=
2.1. Materials The chelating resin used in the sorption experiments was S930 obtained from Purolite International Limited (Hounslow, UK). The main physical and chemical properties of the resin are presented in Table 1. The conversion of the sodium form of the resin into hydrogen form was done with 10% HCl solution, followed by washing with distilled water until the pH of the effluent dropped to neutrality. Then, the resin has been dried at 60 ºC using an oven. Table 1. Characteristic proprieties of the chelating resin used* Polymer matrix structure Functional groups Ionic form (as shipped) pH range (operating): H+ form, Na+ form Maximum operating temperature Particle size range Total exchange capacity
Macroporous styrene divinylbenzene Iminodiacetic acid Na+ 2 - 6; 6 - 11 70ºC + 1.0mm
