Complexing of heavy metals with phosphates
Abstract
This study investigated the effectiveness of triple superphosphate (TSP) and trisodium phosphate to precipitate heavy metals from solution and simultaneously produce a non-hazardous sludge. The results showed that reaction pH, whether it was 8.5 or 9.5, was not a factor in heavy metal removal nor was the source of heavy metal. Order of chemical addition did not affect heavy metals precipitation nor the toxicity of the resulting sludge. Reaction time did not affect heavy metals precipitation for reaction times greater than five minutes. Water hardness also had no affect on the removal of nickel. Phosphate source was a factor in heavy metal precipitation and the wastewater phase of the research indicated that trisodium phosphate was the better source. However, leachability tests run on the resulting sludge indicated that TSP was the better phosphate choice. Phosphate concentration also affected the removal of heavy metals. The research indicated that lesser amounts of phosphate removed more heavy metals and as the initial heavy metals concentration increased, heavy metal removal also increased. Mixed metal solutions affected the removal of heavy metal but not consistently. The removal of copper was unaffected by mixed metal solutions, whether TSP or trisodium phosphate was the phosphate source. The removal of nickel was affected by mixed metal solutions. When either phosphate source was added, the amount of nickel removed from a mixed metal solution increased (over that of nickel in a single metal solution). The removal of zinc was not affected by a mixed metal solution when the phosphate source was TSP, but was affected when trisodium phosphate was the phosphate source (the removal increased). An EP non-toxic, i.e., non-hazardous, sludge was obtained when the phosphate source was TSP. When used in the wastewater treatment, TSP retained 85 percent of the original heavy metal (zinc) in the resulting sludge. In comparison, the zinc hydroxide sludge leached out 91.5 percent of the original zinc. Trisodium phosphate retained 23.5 percent of the original zinc.
Degree
Ph.D.
Advisors
Etzel, Purdue University.
Subject Area
Sanitation|Civil engineering
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