Abstract
The purification of hydrometallurgical process solutions by Fe(III) precipitation is a common and large-scale industrial operation. This step is notorious for valuable metal loss occurring with the iron precipitation product, which is usually directed to tailings. In this study, factors affecting Fe(III) precipitation and associated copper loss were studied in synthetic process solutions using statistical methods. The variables studied were: Initial acid concentration, retention time, seed addition, and initial Fe(III), Cu(II), and chloride concentrations. The importance of each variable and its interaction effects were studied against two responses, i.e., percent of Fe(III) precipitated as hematite and percent of Cu lost to solids. The results showed that a combination of high acid and moderate seeding was required to simultaneously achieve high proportions of Fe(III) precipitated as hematite and lower copper loss to the precipitates. High acid concentrations create low supersaturation for Fe(III), which minimizes the consequences of homogeneous nucleation and favors particle growth.
Highlights
Pressure leaching of sulphide concentrates has emerged as an alternative to roasting or a way to increase the capacity of a hydrometallurgical plant without increasing sulphuric acid production [1]
For scanning electron microscopy (SEM), a small amount of the washed and dried sample was suspended in water and a few drops of the mixture were dried on carbon tape before imaging
The increase in iron precipitation in the presence of CuSO4 was probably due to the formation of bisulphate (HSO4 − ) via the extra sulphate added to the system, which resulted in a decrease in activity of the hydrogen ion
Summary
Pressure leaching of sulphide concentrates has emerged as an alternative to roasting or a way to increase the capacity of a hydrometallurgical plant without increasing sulphuric acid production [1]. Transformation to crystalline products proceeds via two competing mechanisms: (1) Hematite nucleates and grows within the solid precursor by dehydration and an internal rearrangement process and (2) the formation of goethite involves dissolution of iron from ferrihydrite followed by re-precipitation of the crystalline oxide in solution. The increasing depletion of primary copper ores and increasingly stringent environmental regulations necessitate a minimum loss of valuable metal to the residue and a stable product for disposal This potential for a reduction in metal loss is an economic incentive to the operators of medium-temperature leach processes to improve the quality of their Fe precipitates. A systematic (design of experiments) analysis of the process parameters that affect Fe(III) precipitation, and associated copper loss, from sulphate-chloride solutions under medium-temperature conditions was carried out. Multiple regression analysis of the data was employed to develop a best fit mathematical model
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