PRETREATMENT OF WASTE-WATER FROM HEAVY-OIL-PYROLYSIS-GAS-MAKING SYSTEM

It was found that the process of pressure-hydrolysis failed for the tr eatment of a wastewater containing cyanide and nickel from heavy-oil-p yrolysis-gas-making system. The analysis of the wastewater showed the existence of Ni2+,CN-,NH3, Ca2+ and HCO3-. Therefore, the coordinate c ompounds of [Ni(CN)(4)](2-) and [Ni(NH3)(n)](2+) could be expected. Co nsidering the Ca2+ and potential CO32- transformed from HCO3-, it was not surprising that white precipitate blocked the pipeline within the pressure-hydrolysis process under the condition of high pH. A pretreat ment step of calcium removal was suggested. Various factors were inves tigated and optimal operational conditions were concluded. After calci um was removed, the treatment processes were operated successfully and satisfactory results obtained. The residual concentrations of Ni2+ an d CN- could be reduced to meet the discharging standards. (C) 1997 IAW Q. Published by Elsevier Science Ltd.