Utilization of calcium sulfide derived from waste gypsum board for metal-containing wastewater treatment

To achieve recycling of waste gypsum boards (CaSO4), production of calcium sulfide by
reductive decomposition of CaSO4 was investigated and the decomposition product of CaS
was used as a sulfuration agent in the treatment of nickel-containing simulated wastewater. At
the end of the experiment, residual nickel concentration and filtration characteristics of the
slurry formed by adding CaS to the nickel-containing wastewater were investigated.
Regarding the reductive decomposition of CaSO4, it was found that CaS could be effectively
generated by CaSO4 reductive decomposition with graphite and the CaS content in the final
product was greater than 80% when the reductive decomposition was carried out for one hour
at a temperature of 1273 K, under N2 atmosphere.
Then, in the sulfuration treatment of nickel-containing wastewater with CaS, the applicability of
CaS as a sulfuration agent was confirmed and the nickel concentration in the simulated
wastewater was reduced from 100 mg-Ni l-1 to a value below 1.0 mg l-1, when the CaS was
added to the simulated wastewater at CaS to Ni molar ratio of 1.3. Moreover, sulfide slurry
obtained by adding CaS was characterized by lower average specific filtration resistance and
compressibility coefficient, compared to hydroxide slurry formed by the conventional
precipitation treatment.