PubMed · 10132821
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O R Keil, L P Gallagher. 1993. Serious about standards.. https://pubmed.ncbi.nlm.nih.gov/10132821/
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Soil contamination is a major environmental problem due to the ecological threat it poses. In this work, electron probe microanalysis (EPMA), X-ray diffraction (XRD), and leaching studies were employed to explain the different leaching behaviors of non-stabilized and stabilized soils. The applicability of the leaching fluids used in the toxicity characteristic leaching procedure (TCLP) and Australian Standards, AS 4439.1-1997 for assessing the hazards of contaminated soils was investigated as was the leaching of lead from soil stabilized by cement and buffered phosphate techniques. The results showed Pb speciation in the soil highly influenced metal leaching. The synthetic leaching fluids were unable to provide a reliable estimation of Pb concentration in the municipal landfill leachate (ML) due to the absence of organic ligands capable of forming stable complexes with the lead. Water provided the closest representation of lead leaching from the non-stabilized and phosphate stabilized soils while sodium tetraborate buffer was found to be suitable for cement-stabilized soil in a non-putrescible landfill leachate system. A comparison of stabilization methods revealed that the buffered phosphate technique was more suitable for stabilizing the lead in the soil relative to cement stabilization.
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To characterise the coatings formed and to analyse element partitioning between the aqueous and solid phase, suspensions were prepared with four grain sizes of limestone and three different amounts of acidic solution from oxidized pyrite tailings. In all cases, red coatings with three different layers covered the grain surface, sealing off the acidic solution. The inner layer was composed mainly of basaluminite, the middle layer of schwertmannite, and the outer layer of gypsum and jarosite. Zn, Cd and Tl were co-precipitated by Fe and Al; As and Pb were co-precipitated almost completely by Fe; and Cu formed mainly Cu sulphates. All trace elements reached almost total precipitation at pH 6.3, but the precipitation of As and Pb tended to decrease as the pH rose. Consequently, liming should be calculated so that the soil pH does not exceed 6.3. This calculation should take into account that the armouring of the limestone grains can cause underestimations in the amount of liming material needed.