Separation of Cu(ii) from Cd(ii) in sulfate solution using CaCO3 and FeSO4 based on mechanochemical activation

Abstract

Cadmium and its compounds are important resources in different industries; on the other hand, cadmium is one of the most toxic heavy metals which can cause various health problems. Therefore it is important to develop effective methods for the separation of cadmium from other commonly associated metals from the stance of both resource recycling and environmental purification. Lime neutralization (Ca(OH)₂) and ferrite are widely used to precipitate heavy metals. Limestone (calcium carbonate: CaCO₃) is too stable to be used directly for this purpose. Mechanochemical activation was introduced to increase the activity of CaCO₃. Fe(II)sulfate heptahydrate (FeSO₄·7H₂O) was used as a selective precipitation agent. As a result, Cu(II) was preferentially precipitated as (Fe_x,Cu_y)O while the Cd(II) remained in the solution. The residual of Cu(II) ions in solution could be controlled at less than 0.1%, meanwhile more than 90% of Cd(II) ions remained in aqueous solution. Then, Cu(II)–Cd(II) separation was achieved by a simple solid–liquid separation.