Efficiency Of Nanoscale Zero-valent Iron On The Enhanced Low Molecular Weight Organic Acid Removal Pb From Contaminated Soil

Soil washing is a promising soil remediation technology. In order to enhance the remediation efficiency of low molecular weight organic acid (LMWOA) for washing Pb-contaminated soil, mine and farmland soils were selected as test materials to study the Pb removal efficiencies by the mixed solutions of LMWOA and nZVI. A new biological material Phytolacca americana L. was used for treatment of washing wastewater. This study aimed to submit a useful theoretical evidence and technical basis for remediation of Pb-contaminated soil by soil washing. The main results showed as follows:The Pb removal efficiencies by LMWOA washing were obvious promoted after nZVI adding (p<0.05). They were significantly affected by the nZVI doage, pH and washing time.61.89 and 82.30% of Pb could be removed by the mixed solutions of 0.1 g L-1 nZVI and 0.2 M LMWOA washing from mine and farmland soils, respectively. The optimum of pH for washing was 4.0. Second-order model better described the washing process with a higher correlation coefficient (p<0.01). The Pb removal efficiencies of farmland soil were greater than that of mine soil. The mixed solutions of citric acid (CA) and nZVI showed a better washing performance than the mixed solutions of malic acid (MA) and nZVI.The influence of metal fractions and soil fertility before and after washing was investigated. The results showed that the mixed soiltions of nZVI and LMWOA had different efficiencies on the removal of heavy metals and exchangeable and reducible fractions could be more easily washed away. The soil organic matter content obviouely increased (p<0.05) after washing except for single nZVI treatmwnt (p> 0.05). The mixed soiltions of nZVI and LMWOA washing could buffer the lost of nitrogen, phosphorus and potassium compared with washing by single LMWOA.P. americana is a kind of potential material for treatment of heavy metals in the waste solution after soil washing. Biosorbent dosage, pH, initial Pb2+ concentration and contact time had a significant impact on the Pb2+ adsorption efficiency (p< 0.05). The maximum absorption efficiency and capacity(Qmax) of Pb2+ reached 99% and 14.51 mg g-1,respectively.P. americana could effectively adsorb Pb2+ and Zn2+ from the actual waste solution after soil washing. The heavy metal ions (Pb2+, Zn2+, Cd2+ and Cu2+) were comply with relevant standards after adsorption with P. americana.Combining of LMWOA and nZVI would be a promising alternative approach for remediation Pb-contaminated soil and P. americana could be used as a low cost, eco-friendly and effective biosorbent for the Pb(II) removal from aqueous solutions.