Removal of iron ions from industrial copper raffinate and electrowinning electrolyte solutions by chemical precipitation and ion exchange

Abstract

The reduction of iron ions concentration from copper electrowinning electrolyte solution in copper solvent extraction and electrowinning process, is important to maintain good current efficiency. In this study both chemical precipitation (hydroxide and jarosite) and ion exchange methods were investigated using industrial copper raffinate and electrowinning solutions from Sarcheshmeh copper complex, Iran. Batch precipitation and adsorption tests were initially performed before, a fixed bed column was investigated for iron removal by ion exchange. Batch results indicated that with increasing the pH and dilution, improved the iron removal by chemical precipitation methods. Hydroxide and jarosite precipitations were performed efficiently at pHs of 3 and 2 and temperatures of 70°C and 95°C respectively. The iron removal efficiency was greater with jarosite precipitation (∼70%) compared to hydroxide (∼20%) for a particular pH (2). Diluting by 50% increased the removal efficiency up to 150%. Ion exchange results indicated that pH and dilution did not have a significant effect on the efficiency with this method and it practically performed at ambient temperatures. The batch equilibrium and kinetics experiments were performed with Purolite S957 resin and the results showed that the Sips isotherm (the maximum adsorption capacity was 42mg/g) and both the pseudo-nth order (kad=0.00083mg1−n/g1−n·s and n=1.92) and Langmuir-Freundlich kinetics models (kaLF=0.08mLmin-1mg-1,kdLF=0.12min-1 and n=0.12) were able to predict the equilibrium and kinetics data. In the fixed bed column experiments, the effects of parameters such as the volumetric flow rate and bed height on the breakthrough curves were studied. The iron removal efficiency for the industrial solution which included impurities was less than for synthetic solutions. The results showed that the resin selectively removed the iron ions but did not decrease the copper concentration and used resin was completely regenerated by hydrochloric acid (the amount of 5mL/g of resin and concentration of 30wt%) over several regeneration did not significantly alter the sorption capacity. Finally, a mathematical model based on chemical sorption was used to predict the experimental breakthrough curves data and results showed this model accurately predicted the experimental breakthrough curves. Overall, ion exchange was more efficient at iron removal than chemical precipitation.