Investigation of biodegradable polyaspartate as an effective chelant for washing of lead from soil: response surface methodology approach

In this work, a biodegradable chelant (polyaspartate) was synthesised by using L-aspartic via polysuccinimide and used for removal of lead from polluted soil. The interactive effects of operating parameters, polyaspartate dose, metal concentration, polyaspartate/soil ratio, pH and extraction time, were examined via 3⁵ factorial face-centred central composite design matrix and response surface methodology. The examined responses for the two models developed were (i) concentration of extracted Pb in polyaspartate solution and (ii) residual concentration of Pb in the treated soil. The optimal removal efficiency was 90%, which yields 18 mg/L of extracted Pb and 50 mg/kg of residual Pb in the treated soil, at conditions of pH 3, extraction time of 6 h under highest level of initial Pb concentration (500 mg/kg), polymer/soil ratio of 25 and polyaspartate dose of 36 mmol/L. However, at the lowest level of polymer/soil ratio of 5, the maximum removal efficiency dwindled to 59% with higher residual Pb and extracted Pb concentrations of 205 mg/kg and 59 mg/L, respectively. The results showed that higher soil washing efficiency was linked to lower initial pH, increase in initial lead ions concentration and polyaspartate/soil ratio. The study signifies eco-friendly polyaspartate as an efficient chelant for remediation of Pb polluted soil via washing technique.