Bill Batchelor

Hydrogen peroxide decomposition on manganese oxide (pyrolusite): kinetics, intermediates, and mechanism.

The objective of this study is the kinetic interpretation of hydrogen peroxide decomposition on manganese oxide (pyrolusite) and the explanation of the reaction mechanism including the hydroperoxide/superoxide anion. The decomposition of hydrogen peroxide on manganese oxide at pH 7 was represented by a pseudo first-order model. The maximum value of the observed first-order rates constants (k(obs)) was 0.741 min(-1) at 11.8 of [H(2)O(2)]/[triple bond MnO(2)] when [H(2)O(2)]/[triple bond MnO(2)] were ranged from 58.8 to 3.92. The pseudo first-order rate constants (kMnO(2)) approximated as the average value of 0.025 (min mM)(-1) with a standard deviation of 0.003 at [H(2)O(2)]/[triple bond MnO(2)] ranged from 39.2 to 11.8. When [H(2)O(2)]/[triple bond MnO(2)] was 3.92, the rate constants (kMnO(2)) was 0.061 (min mM)(-1) as maximum. Oxygen production showed that the initial rates increased with decreasing [H(2)O(2)]/[triple bond MnO(2)] and the total amounts of oxygen was slightly less than the stoichiometric value (0.5) in most experiments. However, oxygen was produced at more than 0.5 in low [H(2)O(2)]/[triple bond MnO(2)] (i.e. 3.92 and 9.79). The relative production of hydroperoxide/superoxide anion implied that the production increased with low [H(2)O(2)]/[triple bond MnO(2)], and the existence of anions suggested that the mechanism includes propagation reactions with intermediates such as hydroperoxide/superoxide anion in solution. In addition, both [H(2)O(2)] decomposition and the production of anion were accelerated in alkaline solution. Manganese ion dissolved into solution was negligible in neutral and alkaline conditions, but it greatly increased in acidic conditions.

A kinetic model for autotrophic denitrification using elemental sulfur

Increasing prices for methanol and other petrochemicals have decreased the attractiveness of biological dentrification processes which require such compounds. An alternative to such treatment systems is an autotrophic process using enrichment cultures of Thiobacillus denitrificans fed reduced sulfur compounds. Elemental sulfur appears to be the most promising substrate for this system due to its low cost and ease of handling. However, present models for microbial growth are inadequate to describe growth at high biomass density on a water-insoluble solid substrate such as elemental sulfur. This paper presents a model to describe such a system, and experimental evidence of its validity. The model recognizes three steps which could limit the observed rate of denitrification. (1) Sulfur must be solubilized in the attached biofilm and be transported through the film while being simultaneously removed by microbial reaction. (2) Nitrate must be transported from the bulk liquid to the biofilm surface. (3) Nitrate must be transported through the biofilm where it is microbially reduced to nitrogen gas. The model predicts and experimental evidence verifies that the unit rate of denitrification will be proportional to the ratio of the sulfur concentration to the biomass concentration when this ratio is low and nitrate is in excess. At high values of this ratio, the unit rate is observed to approach a maximum as predicted by the model. The accuracy of the models prediction for the dependence of the unit rate of denitrification on the concentration of nitrate could not be evaluated due to very low concentrations of nitrate measured in the steady-state reactors. Available evidence also supports the prediction of the model that, at low values of the sulfur to biomass ratio, the activation energy of the reaction is about half the value that would be observed at higher sulfur to biomass ratios.

Leach models: Theory and application☆

Abstract Mechanistic leach models can be applied to describe performance of solidified wastes in the Toxicity Characteristic Leaching Procedure test. A simple model was modified to describe the effect of inward diffusion of acetic acid from the leaching solution. However, the model did not incorporate changes in the acetic acid concentration that would be observed over time as pH rises. Mechanistic leach models could also be applied to predict long-term leaching, to quantify the relative importance of chemical and physical immobilization mechanisms, to correlate and extrapolate leaching data for various contaminants and binders, and to predict ultimate performance from early characteristics of the solidified waste.

Degradation of vinyl chloride (VC) by the sulfite/UV advanced reduction process (ARP): Effects of process variables and a kinetic model

Vinyl chloride (VC) poses a threat to humans and environment due to its toxicity and carcinogenicity. In this study, an advanced reduction process (ARP) that combines sulfite with UV light was developed to destroy VC. The degradation of VC followed pseudo-first-order decay kinetics and the effects of several experimental factors on the degradation rate constant were investigated. The largest rate constant was observed at pH9, but complete dechlorination was obtained at pH11. Higher sulfite dose and light intensity were found to increase the rate constant linearly. The rate constant had a little drop when the initial VC concentration was below 1.5mg/L and then was approximately constant between 1.5mg/L and 3.1mg/L. A degradation mechanism was proposed to describe reactions between VC and the reactive species that were produced by the photolysis of sulfite. A kinetic model that described major reactions in the system was developed and was able to explain the dependence of the rate constant on the experimental factors examined. This study may provide a new treatment technology for the removal of a variety of halogenated contaminants.

Sorption of selenium(IV) and selenium(VI) to mackinawite (FeS): effect of contact time, extent of removal, sorption envelopes.

Higher concentrations (127, 253 μM) of Se(IV) at pH 8 were completely removed by 0.5 g/L FeS within 120 min. Removal of Se(VI) by FeS at pH 8 was less extensive than removal of Se(IV). Only 10% of the Se(VI) was removed by 1 g/L FeS within 1h. Removal patterns for Se by FeS depend on pH. Removal patterns of Se at pH 7 and pH 8 were best described by BET models for Se(IV) and Freundlich models for Se(VI), while removal patterns of both at pH 9 and 10 were best described by Langmuir models. Sulfate at 1 and 10 mM had negligible effect on removal of Se(IV) by FeS, while sulfate had little effect on removal of Se(VI) by FeS, but there was some indication that sulfate promoted removal of Se(VI) at intermediate concentrations. The test for the effect of pH on sorption of Se(IV) by FeS showed nearly complete removal at all but the high initial pH. When pH was raised back to initial value, greater removals were observed than initially. Mixtures of Se(VI) and FeS showed moderate removal at low pH, a minimum removal near pH 6 and nearly complete removal at high pH. Very high stability was observed with negligible release as pH decreased.

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.

Perchlorate reduction by the sulfite/ultraviolet light advanced reduction process

Advanced reduction processes (ARPs) are a new class of water treatment processes that combine activation methods and reducing agents to form highly reactive reducing radicals that degrade oxidized contaminants. The combination of sulfite with low-pressure ultraviolet light (UV-L) is the most effective ARP tested to date. In this study, batch kinetic experiments were conducted to characterize the kinetics of perchlorate destruction by the sulfite/UV-L ARP. Experimental variables were pH, sulfite concentration, temperature and UV-L irradiance. The rate of perchlorate degradation by sulfite/UV-L increases with increasing pH and temperature and increases with increasing sulfite concentration to a maximum and then decreases due to lack of mixing within the reactor system used. Efficiency of perchlorate degradation was measured as a quantum yield and was observed to decrease with increasing sulfite concentration. The ultimate product of perchlorate degradation by the sulfite/UV-L ARP is chloride, but chlorate was detected as an intermediate.

The diafiltration method for the study of the binding of macromolecules to heavy metals

Abstract A membrane process known as continuous diafiltration has been utilized as an effective method for the study of the binding of macromolecules to ions. Data from one experiment will result in an entire isotherm when temperature and pH are closely controlled. This paper discusses the theory of continuous diafiltration and describes a procedure for quantifying variable membrane rejection behavior. The binding of five heavy metals (Cd, Cu, Ni, Pb, Zn) individually and collectively, to natural lecithin was studied. Copper exhibited stronger binding when it was the lone ion compared to when it was in a mixture of the five metals. Further, the membrane rejected copper at a constant rate of 10% in the first case compared to a variable rate with an average of 79% in the second. This work was performed to characterization the binding of lecithin to heavy metals as a step in the development of a treatment technique termed micellar enhanced ultrafiltration.

Mineralogical alterations that affect the durability and metals containment of aged solidified and stabilized wastes

Detailed research on the weathering and degradation of solidified and stabilized wastes once treated materials have been buried is lacking, and published data to verify the long-term performance and durability of landfilled treated wastes over time are still only limited. Optical and electron microscopy techniques were used in this study to evaluate features associated with metal-bearing contaminated soil and industrial wastes that have been solidified and stabilized with Portland cement and stored outdoors, archived in the laboratory, or buried on site. Results show that although the extent of degradation after 6 years is considered slight to moderate, the same environmental factors that affect the durability of concrete also must be considered when evaluating the durability and permanence of cement-stabilized and solidified wastes. Furthermore, evaluations of durability and permanence cannot be based on leaching and chemistry analyses alone. The use of all levels of microscopic analyses are needed to accurately evaluate the long-term performance of solidification/stabilization technologies. In addition, regulations for the on-site burial of treated wastes, even after they are rendered nonhazardous, are needed. Burial of cement-based solidified and stabilized wastes in deleterious environmental zones, such as acid or saline soil, as well as fluctuating groundwater systems is not recommended.

MICELLAR-ENHANCED ULTRAFILTRATION OF HEAVY METALS USING LECITHIN

Abstract Conventional treatment methods for removal of heavy metals from metal finishing operations are usually energy-intensive and costly. Micellar-enhanced ultrafiltration (MEUF) with synthetic surfactants is a recently developed technique which can remove heavy metals and other small molecular weight ions from wastestreams at relatively lower costs and without a phase change. Lecithin, a natural, inexpensive, nontoxic, and biodegradable surfactant exhibits emulsifying characteristics which can be used in a MEUF. The binding of various lecithins to cadmium, copper, lead, nickel, and zinc—in a mixture and individually—was studied using a continuous diafiltration method. This technique uses small volumes of toxic waters and produces an entire isotherm with just one experiment. In the presence of all five heavy metals, the lecithin in this study showed the following affinity: Cu > Cd ∼ Zn > Ni. In experiments when only one metal was present, lecithin exhibited the following affinity: Ni > Cu ∼ Zn > Cd. Le...