Oste Leonard A, Lexmond Theo M, Van Riemsdijk Willem H
Department of Environmental Sciences, Wageningen Univ., The Netherlands.
J Environ Qual. 2002 May-Jun;31(3):813-21. doi: 10.2134/jeq2002.8130.
In situ immobilization of heavy metals in contaminated soils is a technique to improve soil quality. Synthetic zeolites are potentially useful additives to bind heavy metals. This study selected the most effective zeolite in cadmium and zinc binding out of six synthetic zeolites (mordenite-type, faujasite-type, zeolite X, zeolite P, and two zeolites A) and one natural zeolite (clinoptilolite). Zeolite A appeared to have the highest binding capacity between pH 5 and 6.5 and was stable above pH 5.5. The second objective of this study was to investigate the effects of zeolite addition on the dissolved organic matter (DOM) concentration. Since zeolites increase soil pH and bind Ca, their application might lead to dispersion of organic matter. In a batch experiment, the DOM concentration increased by a factor of 5 when the pH increased from 6 to 8 as a result of zeolite A addition. A strong increase in DOM was also found in the leachate of soil columns, particularly in the beginning of the experiment. This resulted in higher metal leaching caused by metal-DOM complexes. In contrast, the free ionic concentration of Cd and Zn strongly decreased after the addition of zeolites, which might explain the reduction in metal uptake observed in plant growth experiments. Pretreatment of zeolites with acid (to prevent a pH increase) or Ca (to coagulate organic matter) suppressed the dispersion of organic matter, but also decreased the metal binding capacity of the zeolites due to competition of protons or Ca.
原位固定污染土壤中的重金属是一种改善土壤质量的技术。合成沸石是潜在有用的重金属结合添加剂。本研究从六种合成沸石（丝光沸石型、八面沸石型、X型沸石、P型沸石和两种A型沸石）和一种天然沸石（斜发沸石）中选出了对镉和锌结合最有效的沸石。A型沸石在pH值为5至6.5之间似乎具有最高的结合能力，且在pH值高于5.5时稳定。本研究的第二个目标是研究添加沸石对溶解有机物（DOM）浓度的影响。由于沸石会提高土壤pH值并结合钙，其应用可能会导致有机物分散。在一项批量实验中，由于添加了A型沸石，当pH值从6增加到8时，DOM浓度增加了5倍。在土壤柱渗滤液中也发现DOM大幅增加，尤其是在实验开始时。这导致了由金属-DOM络合物引起的更高的金属淋溶。相比之下，添加沸石后镉和锌的自由离子浓度大幅下降，这可能解释了在植物生长实验中观察到的金属吸收减少的现象。用酸（以防止pH值升高）或钙（以凝聚有机物）对沸石进行预处理可抑制有机物的分散，但由于质子或钙的竞争，也会降低沸石的金属结合能力。
