Binglu Deng,Xingqiu Zhou,Xingjian Yang,Zhi Dang,Guining Lu
ABSTRACT This study reports on the adsorption of polychlorinated biphenyls (PCBs) by powder activated carbon (PAC) in soil washing eluents containing tween-80 surfactant micelles. Factors influencing of adsorption were studied (i.e., time, adsorbents doses, molecular structure of different PCBs congeners, dynamic and thermodynamic models). The adsorption of PCBs on nano bamboo charcoal (NBC) was compared with those on PAC. Finally, the prospect for recycling soil eluents was explored. We found that the PAC and NBC were both effective in removal of 12 mg/L PCBs in soil washing eluents. The results of the adsorption kinetics showed that both materials have different adsorption rate controlling step, the particles diffusion became adsorption rate controlling step of NBC while particle diffusion and adsorption reaction like chemical bonding reactions co-control the adsorption rate of PAC. The adsorption of PCBs on PAC was probably chemisorption through interaction between aromatic rings and oxygen-containing functional groups while the adsorption on NBC was mainly physisorption by micropore filling. After the PAC treatment, the residual tween-80 in the eluents was 27.78% (total mass ratio). The addition of acetone to break micelles before adsorption could increase the recovery of tween-80 to 73.30% while PCBs removal rate could still reach 78.06%. Therefore, the surfactant solutions can be reused after adsorption. The studies provide valuable information on the adsorption of PCBs by PAC in soil washing eluents, which may improve the utilization and selection of PAC in the recovery of soil washing eluents.
Soil washing is an effective remediation method to remove heavy metals from contaminated soil. However, it produces wastewater that contains large amounts of heavy metals, which lead to serious pollution. This study investigated the removal of vanadium (V) from synthetic soil washing effluent using BOF steel slag. The effects of particle size, slag dosage, initial pH, and initial vanadium concentration on removal behavior were studied. Adsorption kinetics and isotherms were also analyzed. The results showed that the vanadium removal efficiency increased as the steel slag particle size decreased and as the amount of slag increased. The initial pH and vanadium concentration did not play key roles. At the optimum particle size (<0.15 mm) and dosage (50 g/L), the removal rate reached 97.1% when treating 100 mg/L of vanadium. The influence of the washing reagent residue was studied to simulate real conditions. Citric acid, tartaric acid, and Na 2 EDTA all decreased the removal rate. While oxalic acid did not have negative effects on vanadium removal at concentrations of 0.05–0.2 mol/L, which was proved by experiments using real washing effluents. Considering both soil washing effect and effluent treatment, oxalic acid of 0.2 mol/L is recommended as soil washing reagent.
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