Remediation of Zn(II)- and Cu(II)-Contaminated Soil Using Citric Acid and Citric Acid-Containing Wastewater

This study investigated the desorption behavior of heavy metals, Zn(II) and Cu(II), in the contaminated soil using citric acid and citric acid-containing wastewater (CACW). Four influence factors, including soil contamination levels, dosage of citric acid, reaction time and soil pH were taken into account. Using the citric acid, the desorption reaction with heavy metals was rapid (i.e., less than 2 h). The removal percentage of Zn(II) and Cu(II) reached more than 90% for one type of Suzhou clay with a pH value of 6.58 and a contaminated level of Zn > 2.7 mg/g and Cu > 3.3 mg/g. The increase of soil pH inhibited the metal desorption. The desorption behavior predicted by Visual MINTEQ was in good agreement with the experimental results. The desorption behavior of Zn(II) and Cu(II) was governed by the affinity of sorption sites for heavy metals and the chelating of organic ligands. Soil contamination levels and contact time were investigated when using CACW as the desorbent. It was concluded that CACW was also effective in extracting Zn(II) and Cu(II) from soil surface. When the contact time between CACW and contaminated soil reached 2 h, the removal percentage of Zn(II) and Cu(II) increased to 33% and 60%, respectively. As a result, CACW that is usually treated as a waste product can be a promising washing solution for soil remediation.