Comparative investigation of N,N′-bis-(dithiocarboxy)piperazine and diethyldithiocarbamate as precipitants for Ni(II) in simulated wastewater

The performances of a coordination polymerization precipitant, N,N′-bis-(dithiocarboxy)piperazine (BDP) were compared with the widely used heavy metal precipitant, diethyldithiocarbamate (DDTC), through the treatment of three kinds of nickel-containing wastewaters, NiSO4, nickel citrate (NiCA) and Ni2+-dye. Results indicated that both BDP and DDTC at their stiochiometric doses could reduce 50.00 mg l−1 free nickel(II) to lower than 1.0 mg l−1 (discharge limit of nickel ions in China) and 10% precipitants doses increase could treat NiCA containing 50.00 mg l−1 Ni2+ to meet the discharge limit. But [NiBDP]n coordination polymerization precipitates had more rapid settling speed than Ni(DDTC)2 precipitates. It was also observed that BDP could still partly remove Reactive Brilliant Red X-3B from Ni(II)-dye integrated wastewater through the adsorption of the precipitates [NiBDP]n, in addition to precipitating Ni(II). A 1:1 stiochiometric dose of BDP/Ni(II) could decrease Ni(II) from 50.00 to 0.87 mg l−1, and simultaneously reduce the dye from 30.00 to 19.52 mg l−1.