A study of the effect of using thiourea as a sulfide donor for metal sulfide precipitation from waste waters

Abstract

A two phase study was made to determine the efficacy of thiourea as a sulfide donor in the precipitation of metal sulfides from solution. The first phase of the study focused on the effect of thiourea on individual ions and combinations of ions in the determination of general procedures for removal of metals from solution. The next phase of the study evaluated these procedures on actual waste streams supplied by the US Bureau of Hines Research Center in Reno, Nevada, USA. In the first phase, copper, zinc, lead, mercury, and cadmium readily formed sulfide precipitates that filtered well when the pH was raised to a range of 9.5 to 1 0 .0 before the thiourea was added. When copper and chloride ions were both present, the precipitation of [Cu(tu) 3 lC] occurred providing an excellent nucleation point for sulfide formation. The only metal studied which was not affected by these procedures was arsenic which remained in solution. From the combination experiments it was concluded that the presence of any of the sulfide precipitates aided in the filtration of all metal precipitates. The optimal removal of metal from four USBH samples came with these procedures when milk of lime was used as the base. Overall removal of metal ions (except arsenic) was between 95 and 100 percent.