Desorption characteristics of Cr(III), Mn(II), and Ni(II) in contaminated soil using citric acid and citric acid-containing wastewater

Abstract

Heavy metal-contaminated soil and wastewater have been attracting an increasing amount of attention due to the potential threat to the surrounding environment and human health. Thus, in this study, citric acid (CA) and citric acid-containing wastewater (CACW) were selected for an evaluation of the influence of the contamination level of the soil, the concentration of citric acid, the contact time, the soil pH, and the ionic interaction on the desorption characteristics of three heavy metals (i.e., Cr(III), Mn(II), and Ni(II)). According to the experimental results, a high concentration of citric acid, an acidic condition, a low level of contamination, and a lengthy contact time were found to be beneficial for desorbing the heavy metals from the contaminated soil. Based on the experimental and calculated results, the H+ ions and organic ligands made substantial contributions to the release and adsorption of the heavy metals. The metal ions on the low selectivity sorption sites were leached out earlier than those on the high selectivity sorption sites. The removal percentages of Cr(III), Mn(II), and Ni(II) using CA with a contact time of 6 h were 39.9%, 77.0%, and 62.8%, respectively. By using the CACW as a desorbent, the removal percentages of Cr(III), Mn(II), and Ni(II) with a contact time of 6 h reached 21.4%, 26.9%, and 63.4%, respectively. This suggests a promising practical application of CACW for removing heavy metals from contaminated soil.