Mechanochemical disproportionation reaction of sulfur on Bi2O3 to synthesize Bi2O2S for simultaneous removals of Cu2+ and Cl- from waste solution

As to chemical precipitation for heavy metal removals, sulfide formations will give much lower concentrations of remaining heavy metals and the accompanying salts in the solutions than alkaline neutralization due to much smaller constants of solubility products of the precipitates. However, the preparation of sulfide precipitant such as Na2S by reducing the sulfate with carbon at high temperature is very environmentally risky and bad in cost performance. In this regard, a new approach is proposed just by co-grinding sulfur with bismuth oxide (Bi2O3) with an aid of NaOH to induce a disproportionation reaction of sulfur to prepare Bi2O2S, which can precipitate both Cu2+ and Cl- in case of CuCl2 in the solution at the same time. Under the optimized experimental conditions, removal efficiencies of Cu2+ and Cl- as high as 99.83% and 98.17%, respectively have been achieved at one step. Bi2O2S has a layered structure composed of [Bi2O2](2+) and S2- layers by weak electrostatic interaction. Through the exchange of Cl- to S2-, two kinds of precipitates as BiOCl and copper sulfide can be obtained, offering a new concept to remove both cations and anions simultaneously for the treatment of wastewater, besides the environment-friendliness of the synthesis process itself.

Automated summary

The new method of preparing Bi2O2S has proven to be effective in removing Cu2+ and Cl- simultaneously from solutions, offering a new concept for the treatment of wastewater by removing both cations and anions at the same time.