Paul F. Sanders

Adsorption/desorption Isotherms of Hg(ii) by Soil

The processes of adsorption and desorption of Hg(II) by 15 soils were investigated. Within an initial Hg solution concentration range of 1.0 × 10-7 to 1.1 × 10-4M, all soils with a large organic matter content (> 11.0 g C kg-1) had an S-type isotherm, whereas all soils with a low organic matter cont

Interaction of Hg(II) with soil-derived humic substances

Abstract The complexation of Hg(II) with soil-derived humic substances was investigated using an iodide selective electrode. Humic substances were titrated with Hg(II) at fixed pH values, 4, 5, and 6. The binding behavior was successfully described with a continuous multiligand distribution model, which incorporated proton competitive binding and ionic strength effects. The parameters obtained from the three titration curves at different pH values were very similar with a Hg binding constant, 4.69 ± 0.19. Less Hg(II) was bound by humic substances at lower pH values due to competitive binding of protons.

Chromium leaching behavior in soil derived from chromite ore processing waste

To obtain information for the remediation design of chromium waste sites, the leaching behavior of chromium in chromium-contaminated soil (Cr-soil) derived from chromium ore processing residue (COPR) was investigated. Batch leaching experiments were conducted using simulated rainwater as the leaching solution with pH adjusted to cover a range from 2.0 to 12.0 No Cr(VI) was detected in the leachate at low pH (<2.5). This may be attributed to adsorption of Cr(VI) onto the soil surface and/or reduction of Cr(VI) to Cr(III) by organic matter and/or by ferrous iron (two other major components of the soil); these processes are favored at low pH. Significant amounts of Cr(VI) were leached between pH 4.5 and 12. Results from leaching experiments indicate that approximately 1% of total Cr (26 mg/g) is readily leachable. The major chromium form in Cr-soil was identified as chromite using X-ray diffraction analysis (XRD). The forms of leachable chromium cannot be identified. It can only be hypothesized that Cr(VI) is leached by a dissolution of the chromate salts and attenuated by adsorption/desorption, precipitation, and redox processes that may occur in the soil-water system. Removal of the organic matter from the Cr-soil increases the amount of Cr(VI) leached over the entire pH range, suggesting that the organic matter can reduce Cr(VI) present in the solution. Cr(III) leaching behavior was also investigated as a function of pH. Cr(III) was found in solution at pH < 5. The amount of Cr(III) leached was controlled by the solubility of Cr(III) precipitates, the extent of Cr(VI) reduction, and the magnitude of Cr(III) adsorption onto the soil surface. No Cr(III) was detected between pH 4.5 and 12 which can be attributed to the presence of insoluble precipitates such as Cr(OH)3(s) and CrxFe1−x(OH)3(s) and the adsorption of Cr(III) species onto the soil particle surface.

Soil Partition Coefficients for Cd by Column Desorption and Comparison to Batch Adsorption Measurements

Desorption of metals from contaminated soils is the initial step in a transport pathway that may ultimately result in contamination of groundwater. Because partition coefficients can be obtained easily from batch adsorption measurements, it is desirable to utilize them if they provide a good estimate of the concentration of metal that can desorb from the soil. Batch adsorption experiments were conducted as a function of pH and metal concentration for a series of eastern United States acidic soils. For comparison purposes, column desorption studies were also carried out as a function of flow rate and metal loading. Eluantsamples were collected at several elution volumes for each of several column flow rates. These column eluant data were treated by a double extrapolation technique to evaluate the partition coefficient obtained under desorption conditions. The apparent partition coefficient increased with increasing column velocity and duration of flow. For each flow rate, the results were extrapolated to that for zero time. These zero-time partition coefficients were then extrapolated to zero flow. The zero-time, zero-flow desorption results from the column data were compared tothoseforthe batch adsorption equilibrium. The partition coefficient obtained for batch adsorption provided a good estimate of the value obtained for desorption of the cadmium contaminant in the dynamic system. The slope of the regression of column K d versus batch K d values was greater than 0.90.

Particle-Size Distribution of Chromium: Total and Hexavalent Chromium in Inspirable, Thoracic, and Respirable Soil Particles from Contaminated Sites in New Jersey

Chromate slag is found mixed with soil at several sites in New Jersey. Previous analyses of the contaminated soil were limited to particle sizes > 30 μm. This study focuses on the inspirable, thoracic, and respirable particles that would enter the human respiratory tract, should the contaminated soil become airborne. This article discusses the soil-sampling procedure used at a slag-contaminated site and a site with visible hexavalent chromium crystals. In addition, the drying and sieving procedures and the techniques needed to resuspend the contaminated dust in a sealed chamber are described for aerodynamic size fractionation (30, 10, and 2.5 μm). The resuspended dust was collected on filters and analyzed for 38 elements by x-ray fluorescence (XRF). Wet chemistry techniques were used to measure total extractable and hexavalent chromium. It was found that 1.6% of the slag had a particle aerodynamic diameter (at 50% cut-point) d 50 = 30 μm, of that 1.1% was d 50 = 10 μm and 0.26% was d 50 = 2.5 μm. Total ch...

Calculation of soil cleanup criteria for volatile organic compounds as controlled by the soil‐to‐groundwater pathway: Comparison of four unsaturated soil zone leaching models

Abstract Four computer models that predict leaching of chemicals in the unsaturated soil zone were used to calculate example soil cleanup criteria for volatile organic compounds, using a hypothetical environmental scenario. The criteria were calculated so that allowable groundwater concentrations for the chemicals were not exceeded. The models used were the Pesticide Root Zone Model (PRZM) and the Seasonal Soil Compartment Model (SESOIL) from the U.S. Environmental Protection Agency, the Sanitary Landfill Model (SLM1) from Oregon State University, and the Integrated Moisture and Aqueous Contaminant Transport model (IMPACT) under development for the State of New Jersey. The hypothetical scenario assumed a water table depth of 10 ft, a contaminated zone from 0 to 4 ft, and sandy loam soil properties. Transport times to groundwater were similar for all four models. The calculated soil criteria for many chemicals using the four models agreed to within an order of magnitude. In a few instances, SLM1 and PRZM p...

Characterization of Ambient Levels of Metals and Polycyclic Aromatic Hydrocarbons for Surficial Soil in the Urban Piedmont Region of New Jersey

This investigation implemented a statistically based sampling program to determine the ambient levels of metals and carcinogenic polycyclic aromatic hydrocarbons in municipalities that meet urban center population criteria within the Piedmont Region of New Jersey. New Jersey Department of Environmental Protection (NJDEP)`s geographic information system (GIS) and on-line aerial photography were used in the sampling sites selection process. For surveying of sampling locations, Global Positioning System (GPS) technology was used. For each location, 1 sample was collected at 0--15.2 cm and analyzed for 23 target analyte list metals, 6 carcinogenic polycyclic aromatic hydrocarbons, total organic carbon, pH, loss on ignition, and particle size. Detected concentrations would represent naturally occurring levels plus those resulting from diffuse anthropogenic pollution (DAP). Arsenic, Cadmium, beryllium, and lead were detected in 13% of soil samples at concentrations above state-proposed cleanup criteria. Carcinogenic polycyclic aromatic hydrocarbons were also detected in 18% of the samples at concentrations above state proposed cleanup criteria.