Biomedical subjects

Bill Batchelor

Publications and source records attributed to Bill Batchelor.

7 recordsLinked to original sources

PubMed2003

Reductive capacity of natural reductants.

Reductive capacities of soil minerals and soil for Cr(VI) and chlorinated ethylenes were measured and characterized to provide basic knowledge for in-situ and ex-situ treatment using these natural reductants. The reductive capacities of iron-bearing sulfide (pyrite), hydroxide (green rust; GR(SO4)), and oxide (magnetite) minerals for Cr(VI) and tetrachloroethylene (PCE) were 1-3 orders of magnitude greater than those of iron-bearing phyllosilicates (biotite, vermiculite, and montmorillonite). The reductive capacities of surface soil collected from the plains of central Texas were similar and slightly greater than those of iron-bearing phyllosilicates. The reductive capacity of iron-bearing soil minerals for Cr(VI) was roughly 3-16 times greater than that for PCE, implying that Cr(VI) is more susceptible to being reduced by soil minerals than is PCE. GR(SO4) has the greatest reductive capacity for both Cr(VI) and PCE followed by magnetite, pyrite, biotite, montmorillonite, and vermiculite. This order was the same for both target compounds, which indicates that the relative reductive capacities of soil minerals are consistent. The reductive capacities of pyrite and GR(SO4) for chlorinated ethylenes decreased in the order: trichloroethylene (TCE) > PCE > cis-dichloroethylene (c-DCE) > vinyl chloride (VC). Fe(II) content in soil minerals was directly proportional to the reductive capacity of soil minerals for Cr(VI) and PCE, suggesting that Fe(II) content is an important factor that significantly affects reductive transformations of target contaminants in natural systems.

Carcinogens, Environmental↗

PubMed2002

Abiotic reductive dechlorination of chlorinated ethylenes by iron-bearing soil minerals. 2. Green rust.

Abiotic reductive dechlorination of chlorinated ethylenes by the sulfate form of green rust (GR(SO4)) was examined in batch reactors. Dechlorination kinetics were described by a modified Langmuir-Hinshelwood model. The rate constant for reductive dechlorination of chlorinated ethylenes at reactive GR(SO4) surfaces was in the range of 0.592 (+/-4.4%) to 1.59 (+/-6.3%) day(-1). The specific reductive capacity of GR(SO4) for target organics was in the range of 9.86 (+/-10.1%) to 18.0 (+/-4.3%) microM/g and sorption coefficient was in the range of 0.53 (+/-2.4%) to 1.22 (+/-4.3%) mM(-1). Surface area-normalized pseudo-first-order initial rate constants for chlorinated ethylenes by GR(SO4) were 3.4 to 8.2 times greater than those by pyrite. Chlorinated ethylenes were mainly transformed to acetylene, and no detectable amounts of chlorinated intermediates were observed. The rate constants for the reductive dechlorination of trichloroethylene (TCE) increased as pH increased (6.8 to 10.1) but were independent of solid concentration and initial TCE concentration. Magnetite and/or maghemite were produced by the oxidation of GR(SO4) by TCE. These findings are relevant to the understanding of the role of abiotic reductive dechlorination during natural attenuation in environments that contain GR(SO4).

Acetylene↗

PubMed2002

Abiotic reductive dechlorination of chlorinated ethylenes by iron-bearing soil minerals. 1. Pyrite and magnetite.

Abiotic reductive dechlorination of chlorinated ethylenes (tetrachloroethylene (PCE), trichloroethylene (TCE), cis-dichloroethylene (cis-DCE), and vinyl chloride (VC)) by pyrite and magnetite was characterized in a batch reactor system. Dechlorination kinetics was adequately described by a modified Langmuir-Hinshelwood model that includes the effect of a decreasing reductive capacity of soil mineral. The kinetic rate constant for the reductive dechlorination of target organics at reactive sites of soil minerals was in the range of 0.185 (+/- 0.023) to 1.71 (+/- 0.06) day(-1). The calculated specific reductive capacity of soil minerals for target organics was in the range of 0.33 (+/- 0.02) to 2.26 (+/- 0.06) microM/g and sorption coefficient was in the range of 0.181 (+/- 0.006) to 0.7 (+/- 0.022) mM(-1). Surface area-normalized pseudo-first-order initial rate constants for target organics by pyrite were found to be 23.5 to 40.3 times greater than those by magnetite. Target organics were mainly transformed to acetylene and small amount of chlorinated intermediates, which suggests that beta-elimination was the main dechlorination pathway. The dechlorination of VC followed a hydrogenolysis pathway to produce ethylene and ethane. The addition of Fe(II) increased the dechlorination rate of cis-DCE and VC in magnetite suspension by nearly a factor of 10. The results obtained in this research provide basic knowledge to better predict the fate of chlorinated ethylenes and to understand the potential of abiotic processes in natural attenuation.

Ethylenes↗

PubMed2002

Effects of ferrous iron and molecular oxygen on chromium(VI) redox kinetics in the presence of aquifer solids.

The kinetics and stoichiometry of the reduction of hexavalent chromium (Cr(VI)) with ferrous iron (Fe(II)) were examined in systems with and without aquifer solids. Cr(VI) reduction was rapid in the absence of solids, but demonstrated slower and more complex kinetics in the presence of aquifer solids. The aquifer solids removed Fe(II) from solution and a portion of the reducing capacity of Fe(II) was transferred to the aquifer solids. The solid phases were then able to continue to remove Cr(VI). This suggests in situ treatment of Cr(VI) by Fe(II) injection would be feasible in the aquifer environment. In general, re-oxidation of reduced chromium by molecular oxygen was not observed in our systems over time periods of nearly 1 year, suggesting that the potential for chromium solubilization under these oxidizing conditions will be low. An empirical model was developed to describe the reduction kinetics of Cr(VI) in the presence of solids. The model assumes that the reaction is brought about by pseudo-species of iron that react instantaneously, rapidly and slowly with Cr(VI). A fourth pseudo-species is assumed to be non-reactive. Model coefficients were determined by non-linear regression. The model was able to describe observed concentrations of chromium well, but analysis of model errors indicated the potential existence of a distribution of species with different reaction rates rather than just three distinct species. Another model was developed to predict concentrations of different pseudo-species depending on the total amount of Fe(II) added and the amount of aquifer solids present. This model assumed that pseudo-species could result from intrinsic characteristics of the aquifer solids as well as being formed by addition of Fe(II), which could sorb to the aquifer solids.

Carcinogens, Environmental↗

PubMed2002

A multi-component numerical leach model coupled with a general chemical speciation code.

A multi-component numerical leach model (SBLEM) was developed by coupling a general chemical speciation code with a modified Crank-Nicolson algorithm to determine the leaching behavior of contaminants in stabillized/solidified (s/s) wastes. The thermodynamic database of the speciation code was modified using batch leaching data. SBLEM was evaluated by simulating a dynamic leaching test of cement-treated combined bottom and fly ash from a municipal solid waste (MSW) incinerator. Simulations used an input composition prepared from acid neutralization capacity (ANC) test data of the ash. The results show that SBLEM can reasonably predict the dynamic leaching behavior of metals from the cement-treated ash when the ANC of the ash and pH-solubility curves of metals are well described. This indicates SBLEM simulations may be able to augment or replace experimental leaching tests that can consume a substantial period of time (> 2 months) and in some cases, provide unreliable results.

Forecasting↗

PubMed2002

Reductive dechlorination of chlorinated methanes in cement slurries containing Fe(II).

Degradative solidification/stabilization (DS/S) is a novel remediation technology that combines chemical degradation with conventional solidification/stabilization. The applicability of the Fe(II)-based DS/S to treating chlorinated alkanes was tested by characterizing degradation reactions of carbon tetrachloride (CT) and its daughter products in cement slurries containing Fe(II). Degradation kinetics of CT and chloroform (CF) were generally very rapid with reaction rates comparable to rates that can be obtained with zero-valent iron. Dechlorination reactions of CT proceeded primarily via a hydrogenolysis pathway, which yielded CF and methylene chloride (MC) as major products and chloromethane and methane as minor products. However, reaction pathways other than hydrogenolysis also appeared to be important at very high pH conditions. MC apparently was resistant to dechlorination reactions over a period of about two months. Kinetics of CT and CF transformation were strongly dependent on pH with an optimal value around 13, which was higher than found previously for PCE. When the initial CF concentration varied between 0.01 and 1 mM, and the Fe(II) dose was 104 mM, pseudo-first-order kinetics generally described the degradation reactions of CF. However, there was also some indication of substrate saturation kinetics in these experiments. This suggests that a saturation model would better describe the kinetics in systems with higher concentration of substrates or lower concentration of the reactive surfaces.

Carbon Tetrachloride↗

PubMedDate not supplied

Chloride removal from recycled cooling water using ultra-high lime with aluminum process.

Chloride is a deleterious ionic species in cooling water systems because it promotes corrosion, and most of the scale and corrosion inhibitors are sensitive to chloride concentration in the water. Chloride can be removed from cooling water by precipitation as calcium chloroaluminate [Ca4Al2Cl2(OH)12]. A set of equilibrium experiments and one kinetic experiment were conducted to evaluate chloride removal using the ultra-high lime with aluminum (UHLA) process and to characterize the equilibrium conditions of calcium chloroaluminate precipitation. A total of 48 batch-equilibrium experiments were conducted on a 30 mM NaCl solution over a range of values for lime dose (0 to 200 mM) and sodium aluminate dose (0 to 100 mM). Experimental results showed that the UHLA process can remove chloride and that the formation of a calcium chloroaluminate solid phase is a reasonable mechanism that is able to adequately describe experimental results. An average value of the ion activity product of 10(-94.75) was obtained and can be used as an estimate of the solubility product for Ca4Al2Cl2(OH)12.

Aluminum↗