NaH2PO4 synergizes with organic matter to stabilize chromium in tannery sludge

Heavy metal stabilization is an effective method to treat chromium in tannery sludge . Here we show that mainly investigated NaH 2 PO 4 (MSP) and organic matter (OM) to stabilize chromium in tannery sludge. The experimental investigation revealed that the addition of montmorillonite (MMT) and MSP samples showed a significant increase in the percentage of reducible and oxidizable Cr in the former compared to the samples with the addition of MMT. This is attributed to the formation of Cr–O bond, which allows the MSP to undergo an inner-sphere complexation reaction with the metal oxide of Cr via ligand exchange . Significantly, the MSP moiety adsorbs on the surface of OM through monodentate, which increases the adsorption sites of OM for Cr 6+ and promotes the reduction of Cr 6+ to Cr 3+ . Moreover, PO 4 3− reacts with Cr 3+ to produce CrPO 4 precipitation, thus reducing the free Cr 3+ content. Finally, DFT calculations confirmed that a ternary system is formed between PO 4 3− , OM, and Cr, and the binding energy is negative, which indicated that PO 4 3− could co-stabilize Cr with OM.