Application of response surface methodology for the optimization of lead removal from contaminated soil using chelants

Abstract

The remediation of Pb-contaminated soil has become an international concern in recent decades due to mines exploitation and fertilizer abuse. Batch chemical soil washing experiments were conducted to optimize Pb removal efficiency from contaminated soil by two biodegradable chelants, citric acid (CA) and [S,S]-ethylenediaminedisuccinic acid (EDDS). The influences of chelant concentration, pH and contact time were evaluated. In a single factor test, a maximum Pb removal efficiency of 77.84% was achieved with 100 mM CA solution and pH 2.0 for 60 min, while it reached 81.49% with 400 mM EDDS solution and pH 4.0 for 60 min. Response surface methodology (RSM) based on Box–Behnken design (BBD) was applied to optimize the experimental conditions. The interactions between selective factors were significant (P < 0.05). Polynomial models were developed for the experimental response and optimal conditions were obtained with high determination coefficients (R² ≥ 0.90, P < 0.05). Furthermore, Pb removal efficiencies by CA and EDDS washing were 70.08 and 80.26%, respectively, under optimal conditions, and close to the predicted values (74.49 and 83.95%) from RSM. The results confirmed the accuracy and reliability of the optimization process using RSM. Therefore, response surface methodology is a suitable approach to determine the optimal parameters for chemical soil washing to remediate heavy metal polluted soil using biodegradable chelants.