Remediation from clay soil

Albrecht campaigned against the concept of an acid soil causing poorer crop growth rather, it is the calcium deficiency that needs to be remedied. The acid soil solution dissolves rock particles, such as rock phosphate and limestone, to release beneficial nutrients such as phosphate and calcium respectively. It also mobilizes the other adsorbed ions off the clay-humus colloid. He estimated the optimum ratios of calcium to magnesium and calcium to potassium. These were approximately from 4 1 to 7.5 1, and from 15 1 to 38 1 respectively. The higher the Ca K ratio, the more proteinaceous... 

Thermotech Systems Corporation (Thermotech) has patented a thermal desorption, two-stage tandem soil remediation unit (TDU) that treats and desorbs light and heavy hydrocarbons from contaminated soils, clays, and drilling muds. Thermotech s TDU does not incinerate soil, but rather cleans and recycles it. The technology has been commercially available since 1991. 

Reddy, K. R., Chaparro, C., and Saichek, R. E. (2003a). Iodide-enhanced electrokinetic remediation of mercury-contaminated soils. J. Environ. Eng. 129(12), 1137-1148. Reddy, K. R., Chaparro, C., and Saichek, R. E. (2003b). Removal of mercury from clay... 

Reddy KR, Parupudi US. (1997). Removal of chromium, nickel, and cadmium from clays by in-situ electrokinetic remediation. Journal of Soil Contamination 6(4) 391-407. 

Note that Cs can be removed from collapsed interlayer sites - it just requires that an ion such as NHq be the displacing agent. Indeed, in situ techniques for leaching Cs from soils typically rely on the introduction of NHq into the subsurface as the means for freeing up Cs from clay interlayers. A case can certainly be made for simply leaving the Cs-contaminated soils to remediate themselves ... 

The electrokinetic process will be limited by the solnbUity of the contaminant and the desorption from the clay matrix that is contaminated. Heterogeneities or anomalies in the soil wiU rednce removal efficiencies. Extreme pHs at the electrodes and the may inhibit the system s effectiveness. Electrokinetic remediation is most efficient when the pore water has low salinity. The process requires sufficient pore water to transmit the electrical charge. Contaminant and noncontaminant concentrations effect the efficiency of the process. 

The cost of a vertical Lasagna system was evaluated by DuPont using a cost optimization model. For remediation of TCE to a depth of 40 to 50 ft (12 to 15 m) in clay on a 1-acre (4047-m ) site, costs were estimated to range from 40 to 90/yd ( 52 to 117/m ). Soil properties, depth of contamination, cost of emplacing electrodes and treatment zones, required purge water volume, cleanup time, and cost of electrical power were all included in the estimate (D12500Y, p. 10). 

Electrokinetics is an in situ remediation technology applicable to soil or soil-like material with low hydraulic conductivities (e.g., clay) contaminated with heavy metals, radionuclides, and selected organic pollutants. The technique has been used in the past in the oil recovery industry and to remove water from soils. 

Bioreactors containing an undefined anaerobic consortium reduced TNT to 2,4,6-triaminotoluene (TAT) in the presence of glucose (Daun et al. 1998). The sorption of TAT to montmorillonite clay was irreversible, and the substrate could not be released by solvent extraction or by add or alkaline treatment. Similar results were obtained with humic acids in which covalent reaction with carbonyl or activated C=C bonds bonding presumably occurs (Chapter 3, Section 3.2.4). Results from laboratory experiments using 14C-labeled TNT in reactors to which molasses was added as carbon source showed that after 9 weeks, 83% of the radioactivity was recovered in soil components (humin, humic adds, and fulvic acids) (Drzyzga et al. 1998). These results illustrate the important issue of the association of metabolic products from TNT with soil components which in turn may reduce the effectiveness of remediation. 

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