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Influence of solution acidity and CaCl2 concentration on the removal of heavy metals from metal-contaminated rice soils.
Environ Pollut. 2006 Dec; 144(3):918-25.EP

Abstract

Soil washing is considered a useful technique for remediating metal-contaminated soils. This study examined the release edges of Cd, Zn, Ni, Cr, Cu or Pb in two contaminated rice soils from central Taiwan. The concentrations exceeding the trigger levels established by the regulatory agency of Taiwan were Cu, Zn, Ni and Cr for the Ho-Mei soil and Pb for the Nan-Tou soil. Successive extractions with HCl ranging from 0 to 0.2 M showed increased release of the heavy metals with declining pH, and the threshold pH value below which a sharp increase in the releases of the heavy metals was highest for Cd, Zn, and Ni (pH 4.6 to 4.9), intermediate for Pb and Cu (3.1 to 3.8) and lowest for Fe (2.1), Al (2.2) and Cr (1.7) for the soils. The low response slope of Ni and Cr particularly for the rice soils make soil washing with the acid up to the highest concentration used ineffective to reduce their concentrations to below trigger levels. Although soil washing with 0.1 M HCl was moderately effective in reducing Cu, Pb, Zn and Cd, which brought pH of the soils to 1.1+/-0.1 (S.D.), the concurrent release of large quantities of Fe and Al make this remediation technique undesirable for the rice soils containing high clay. Successive washings with 0.01 M HCl could be considered an alternative as the dissolution of Fe and Al was minimal, and between 46 to 64% of Cd, Zn, and Cu for the Ho-Mei soil and 45% of Pb in the Na-Tou soil were extracted after four successive extractions with this dilute acid solution. The efficacy of Cd extraction improved if CaCl2 was added to the acid solution. The correlation analysis revealed that Cr extracted was highly correlated (P < 0.001) with Fe extracted, whereas the Cu, Ni, Zn, Cd or Pb extracted was better correlated (P < 0.001) with Al than with Fe extracted. It is possible that the past seasonal soil flooding and drainage in the soils for rice production was conducive to incorporating Cr within the structure of Fe oxide, thereby making them extremely insoluble even in 0.2 M HCl solution. The formation of solid solution of Ni with Al oxide was also possible, making it far less extractable than Cd, Zn, Cu, or Pb with the acid concentrations used.

Authors+Show Affiliations

Environmental Engineering Department, Da-Yeh University, Da-Tsuen, ChangHua, Taiwan. skuo@wsu.eduNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article

Language

eng

PubMed ID

16603295

Citation

Kuo, S, et al. "Influence of Solution Acidity and CaCl2 Concentration On the Removal of Heavy Metals From Metal-contaminated Rice Soils." Environmental Pollution (Barking, Essex : 1987), vol. 144, no. 3, 2006, pp. 918-25.
Kuo S, Lai MS, Lin CW. Influence of solution acidity and CaCl2 concentration on the removal of heavy metals from metal-contaminated rice soils. Environ Pollut. 2006;144(3):918-25.
Kuo, S., Lai, M. S., & Lin, C. W. (2006). Influence of solution acidity and CaCl2 concentration on the removal of heavy metals from metal-contaminated rice soils. Environmental Pollution (Barking, Essex : 1987), 144(3), 918-25.
Kuo S, Lai MS, Lin CW. Influence of Solution Acidity and CaCl2 Concentration On the Removal of Heavy Metals From Metal-contaminated Rice Soils. Environ Pollut. 2006;144(3):918-25. PubMed PMID: 16603295.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Influence of solution acidity and CaCl2 concentration on the removal of heavy metals from metal-contaminated rice soils. AU - Kuo,S, AU - Lai,M S, AU - Lin,C W, Y1 - 2006/04/05/ PY - 2005/12/02/received PY - 2006/01/30/revised PY - 2006/02/02/accepted PY - 2006/4/11/pubmed PY - 2006/12/9/medline PY - 2006/4/11/entrez SP - 918 EP - 25 JF - Environmental pollution (Barking, Essex : 1987) JO - Environ Pollut VL - 144 IS - 3 N2 - Soil washing is considered a useful technique for remediating metal-contaminated soils. This study examined the release edges of Cd, Zn, Ni, Cr, Cu or Pb in two contaminated rice soils from central Taiwan. The concentrations exceeding the trigger levels established by the regulatory agency of Taiwan were Cu, Zn, Ni and Cr for the Ho-Mei soil and Pb for the Nan-Tou soil. Successive extractions with HCl ranging from 0 to 0.2 M showed increased release of the heavy metals with declining pH, and the threshold pH value below which a sharp increase in the releases of the heavy metals was highest for Cd, Zn, and Ni (pH 4.6 to 4.9), intermediate for Pb and Cu (3.1 to 3.8) and lowest for Fe (2.1), Al (2.2) and Cr (1.7) for the soils. The low response slope of Ni and Cr particularly for the rice soils make soil washing with the acid up to the highest concentration used ineffective to reduce their concentrations to below trigger levels. Although soil washing with 0.1 M HCl was moderately effective in reducing Cu, Pb, Zn and Cd, which brought pH of the soils to 1.1+/-0.1 (S.D.), the concurrent release of large quantities of Fe and Al make this remediation technique undesirable for the rice soils containing high clay. Successive washings with 0.01 M HCl could be considered an alternative as the dissolution of Fe and Al was minimal, and between 46 to 64% of Cd, Zn, and Cu for the Ho-Mei soil and 45% of Pb in the Na-Tou soil were extracted after four successive extractions with this dilute acid solution. The efficacy of Cd extraction improved if CaCl2 was added to the acid solution. The correlation analysis revealed that Cr extracted was highly correlated (P < 0.001) with Fe extracted, whereas the Cu, Ni, Zn, Cd or Pb extracted was better correlated (P < 0.001) with Al than with Fe extracted. It is possible that the past seasonal soil flooding and drainage in the soils for rice production was conducive to incorporating Cr within the structure of Fe oxide, thereby making them extremely insoluble even in 0.2 M HCl solution. The formation of solid solution of Ni with Al oxide was also possible, making it far less extractable than Cd, Zn, Cu, or Pb with the acid concentrations used. SN - 0269-7491 UR - https://www.unboundmedicine.com/medline/citation/16603295/Influence_of_solution_acidity_and_CaCl2_concentration_on_the_removal_of_heavy_metals_from_metal_contaminated_rice_soils_ L2 - https://linkinghub.elsevier.com/retrieve/pii/S0269-7491(06)00094-7 DB - PRIME DP - Unbound Medicine ER -