Calcium sulfide-organosilicon complex for sustained release of H2S in strongly acidic wastewater: Synthesis, mechanism and efficiency

Sulfide precipitation is an efficient method to remove Cu(II) and As(III) from strongly acidic wastewater, but the instantaneous release of H 2 S from traditional sulfuration reagents causes serious H 2 S pollution. Moreover, the obtained precipitates are mixtures of CuS and As 2 S 3 , leading to difficulties in resource recovery. In this study, a calcium sulfide-organosilicon complex (CaS-OSCS), in which CaS was coated into a matrix of {[O 1.5 Si(CH 2 ) 3 NH]CS} n (OSCS) via the coordination bonding, was developed. OSCS, as a matrix of CaS-OSCS, can ensure the sustained and stable release of H 2 S under strongly acidic conditions owing to its low swelling (1.75% swelling ratio) and excellent acid resistance. The release longevity of H 2 S from CaS-OSCS extended from 5 min up to 50 min compared with that from CaS because the hydrophobic OSCS prevented solution diffusing to the pores of CaS-OSCS and thus slowed down the hydrolysis of CaS in pores. 99% of Cu(II)/As(III) was precipitated without H 2 S escape, and the dosage of sulfuration reagents was reduced by 30%. In addition, CaS-OSCS improved the selective separation of copper from wastewater, and a separation factor between Cu(II) and As(III) reached 2376. This study provides a potential approach for the elimination of H 2 S pollution and selective recovery of copper.