Removal of Heavy Metal Ions from Wastewaters: An Application of Sodium Trithiocarbonate and Wastewater Toxicity Assessment.

The synthesis and application of sodium trithiocarbonate (Na ₂ CS ₃ ) for the treatment of real galvanic wastewater in order to remove heavy metals (Cu, Cd and Zn) was investigated. A Central Composite Design/Response Surface Methodology (CCD/RSM) was employed to optimize the removal of heavy metals from industrial wastewater. Adequacy of approximated data was verified using Analysis of Variance (ANOVA). The calculated coefficients of determination ( R ² and R ² _adj ) were 0.9119 and 0.8532, respectively. Application of Na ₂ CS ₃ conjugated with CCD/RSM allowed Cu, Cd and Zn levels to be decreased and, as a consequence, ∑ _Cu,Cd,Zn decreased by 99.80%, 97.78%, 99.78%, and 99.69%, respectively, by using Na ₂ CS ₃ at 533 mg/L and pH 9.7, within 23 min. Implementation of conventional metal precipitation reagents (NaOH, Ca(OH) ₂ and CaO) at pH 11 within 23 min only decreased ∑ _Cu,Cd,Zn by 90.84%, 93.97% and 93.71%, respectively. Rotifer Brachionus plicatilis was used to conduct the assessment of wastewater toxicity. Following the application of Na ₂ CS ₃ , after 60 min the mortality of B. plicatilis was reduced from 90% to 25%. Engagement of Na ₂ CS ₃ under optimal conditions caused the precipitation of heavy metals from the polluted wastewater and significantly decreased wastewater toxicity. In summary, Na ₂ CS ₃ can be used as an effective heavy metal precipitating agent, especially for Cu, Cd and Zn.