Extraction of Nickel from Iron and Cobalt Bearing Sulfate Solutions by Solvent Extraction

Solvent extraction, as commonly applied in hydrometallurgical operations, is a unit operation for the purification and concentration of a wide variety of metals. Many metal separations are being done commercially by extraction of aqueous solutions, such Cu, Co, Zn, U, Mo, W, V, Zr, Hf, Nb, Ta, Ga, Ge, rare earths, and the platinum group metals (PGMs). Solvent extraction is a common form of chemical extraction using organic solvent as the extractant. It is commonly used in combination with other technologies, such as solidification/stabilization, precipitation and electrowinning. In this study, solvent extraction is applied for extracting nickel from sulfate solutions containing iron and cobalt as an example for the cleaning of waste solutions and for increasing solution concentrations after leaching. Di-2-ethylhexyl phosphoric acid (D2EHPA) is used as an extractant for this purpose. Effects of pH, aqueous/organic (A/O) phase ratio, iron and cobalt contents of the solution on nickel extraction efficiency were investigated. The McCabe-Thiele diagrams for extraction and stripping steps were developed to determine the number of stages required. A total of two stages were required for 96.3% of Ni extraction and a total of two stages to strip of nickel with 98% efficiency.