Cadmium removal from organic acid-bearing soil-washing water by magnetic biosorption: Effect of various factors and adsorption isothermal study

Cadmium leaching from contaminated soil by in-situ washing technology may result in huge water effluents contaminated by both cadmium Cd(II) and leaching reagent. This work explored the effect of the presence of eleven organic acids (OAs) (mainly citric acid CA) on Cd(II) biosorption (concentration range: 3-30 mgCd L-1) by magnetic wood (MW). MW was prepared by depositing magnetite on sawdust. MW offers ease of separation of the adsorbent and excellent uptake properties. The studied OAs may be used as washing/leaching reagents of soil contaminated with Cd(II). Effects of pH, Cd(II):CA ratio, stirring Cd(II)/CA before adding MW, type of OA were all studied. The presence of any of the OAs significantly enhanced Cd(II) uptake from water at pH 8.5, 1:3 M ratio (Cd:OA), stirring Cd(II)/OA for 30 min before adding MW. Comparison studies gave the following remarks: Pb(II) exhibited higher tendency than Cd(II) towards MW; Cd(II) showed higher affinity towards magnetite than towards MW; OAs enhanced Cd(II) uptake from 12 and 30 mgCd L-1 solutions by MW (%removal: 93 % and 65 %, respectively). The optimum method was applied on OA-bearing soil-washing water (SWW) containing 16 mgCd L-1, where total Cd(II) removal was achieved after three successive adsorptions. All adsorption results were modeled by Langmuir and Freundlich equation. Citric acid-modified magnetic wood (CA-MW) was compared with our optimum procedure where the former exhibited more adsorption capacity (Q(max) = 32.5 mgCd L-1) than the presence of CA (Q(max) = 16.3 mgCd L-1). MW may be used for Cd(II) removal from OA-bearing SWW.