Effective purification of high concentration chromium-containing wastewater and preparation of chromium ferrite

Abstract

The formation of valuable ferrite in one step by adding ferrous sulfate to chromium-containing wastewater without adjusting to acidic conditions was studied under simple mechanical equipment. The process can not only solve the problem of heavy metals removal from wastewater, but also achieve the purpose of chromium resource recovery. Increasing temperature and pH can further promote the formation of chromium ferrite while prolonging the reaction time has no significant effect on the product’s performance. The response surface method (RSM) was utilized to optimize the process of ferrite formation: the Fe²⁺/Cr⁶⁺ mole ratio of 7, pH value of 10.5, and temperature of 100℃, on which formed ferrite has a high saturation magnetization of 41.28 emu/g with Cr(VI) removal ratio around 100%. TCLP (Toxicity Characteristic Leaching Procedure) tests showed that the chromium concentrations leached from the solid were below the limit of 5 mg/L by USEPA. The molecular formula of chromium ferrite can be expressed as Fe_3-xCr_xO₄ (where x is about 0.45), which has the potential to be recycled as a favorable material. The ferrite process has a low activation energy of 20.8 kJ/mol, which is an economical and environmentally friendly method for synthesizing ferrite from wastewater.