Young Ku

THE EFFECT OF COMPLEXING AGENTS ON THE PRECIPITATION AND REMOVAL OF COPPER AND NICKEL FROM SOLUTION

ABSTRACT This paper addresses the effect of the complexing agents citrate, tartrate, ammonia, phosphate, and EDTA on the removal of copper and nickel from solution using both hydroxide and sulfide precipitation. Both batch and continuous metal sulfide precipitation experiments were performed. Results are presented for the removal of heavy metals and the resulting particle size distributions. The presence of weak complexing agents (citrate, tartrate, ammonia, and phosphate) had a minimal effect on the removal of copper and nickel, while the presence of a strong complexing agent (EDTA) resulted in the residual metal concentration being 1-2 orders of magnitude greater than the case with no complexing agents present. In an open system, the residual nickel concentration increased with increasing reaction time, due to the oxidation of nickel sulfide co nickel sulfate. For copper sulfide precipitation, the presence of complexing agents reduced the precipitate growth rate, nuclei density, and nucleation rate, res...

THE EFFECT OF TARTRATE, A WEAK COMPLEXING AGENT, ON THE REMOVAL OF HEAVY METALS BY SULFIDE AND HYDROXIDE PRECIPITATION

ABSTRACT Industrial vastevaters generated in the electroplating and metal finishing industries typically contain toxic heavy metals. Depending on their origin, these wastewaters may also contain chelating agents, such as EDTA, NTA, citrate, tartrate, and gluconic acid. Although the major effect of complexation is an increase in the solubility of complexed metal ions, significant changes in the precipitation kinetics and particle size distribution may also contribute to the observed precipitation behavior. This paper addresses the effect of a weak complexing agent, tartrate, on the removal of zinc and cadmium using both hydroxide and sulfide treatment. Results are presented on the removal of heavy metals from synthetic plating wastewaters. Poor zinc removals were observed in the presence of tartrate, particularly when larger filter pore sizes were employed. The results suggest that tartrate severely hinders both zinc hydroxide and zinc sulfide precipitation, resulting in the formation of very fine precipit...

Removal of sulfides from waters and wastewaters by activated carbon

The use of activated carbon treatment for removal of sulfides from wastewaters has been shown to be an effective process. Preliminary results show dissolved sulfide reductions of 36 to 95% were achieved using Darco S51 powdered activated carbon at a dosage of 1000 mg/l to treat a synthetic wastewater containing 1–50 mg/l of dissolved sulfide. Experiments were performed over a pH range of 6.0 to 12.0; the minimum residual sulfide concentration is achieved at pH ∼ 8.5. The removal of sulfides by activated carbon can be adequately described using either a Langmuir or Freundlich isotherm. Various brands and types of activated carbon were investigated, resulting in different adsorption characteristics. The rate of sulfide removal is fast, generally reaching equilibrium in a very short time (t < 30 min). Adsorption capacities in the range of 150 to 900 μmol/g of activated carbon were observed resulting in Ce being in the range of 6.8 to 10.0 mg S/l for large applied sulfide concentrations (in the absence of heavy metals). The presence of several foreign ions (NH4+, CN−, etc.) interfered with the removal of dissolved sulfide by activated carbon adsorption due to a competition for the active sites by the sulfide species and the contaminant ions.