Katta J. Reddy

Solubility and mobility of copper, zinc and lead in acidic environments

Understanding the chemical speciation of metals in solution is necessary for evaluating their toxicity and mobility in soils. Soil samples from the Powder River Basin, Wyoming were extracted with distilled deionised H2O. Soil water extracts were subjected to chemical speciation to determine the relative distribution and chemical forms of copper (Cu), zinc (Zn) and lead (Pb) in acidic environments. As pyrite oxidised, the pH decreased from 6.6 to 2.4, concentration of dissolved sulfate (ST) increased from 259 to 4,388 mg L-1 and concentration of dissolved organic carbon (DOC) decreased from 56.9 to 14.4 mg L-1. Dissolved Cu concentrations ranged from 0.06 to 0.42 mg L-1 and dissolved Zn concentrations ranged from 0.084 to 4.60 mg L-1. Dissolved concentrations of Pb were found to be 0.003 to 0.046 mg L-1. Chemical speciation indicated that at near neutral pH, dissolved metal concentration in soil water extracts was dominated by DOC- metal complexes. At low pH, dissolved metal concentration in soil water extracts was dominated by free ionic forms (e.g. Cu2+, Zn2+, Pb2+) followed by ion pairs (e.g. CuSO40, ZnSOinf4sup0, PbSOin4sup0). Results obtained in this study suggest that as soil pH decreased, the availability and mobility of metal ions increased due to the chemical form in which these metal ions are present in soil solutions.

Electrocatalytic reduction of nitrate in water

Nitrate (NO(3)(-)) contamination of groundwater is a common problem throughout intensive agricultural areas (nonpoint source pollution). Current processes (e.g., ion exchange, membrane separation) for NO(3)(-) removal have various disadvantages. The objective of this study was to evaluate an electrocatalytic reduction process to selectively remove NO(3)(-) from groundwater associated with small agricultural communities. A commercially available ELAT (E-Tek Inc., Natick, MA) carbon cloth with a 30% surface coated Rh (rhodium) (1microg x cm(-1)) was tested at an applied potential of -1.5 V versus standard calomel electrode (SCE) with a Pt auxiliary electrode. Electrocatalytic reduction process (electrolysis) of NO(3)(-) was tested with cyclic voltammetry (CV) in samples containing NO(3)(-) and 0.1M NaClO(4)(-). Nitrate and NO(2)(-) concentrations in test solutions and groundwater samples were analyzed by ion chromatography (IC). The presence of Rh on the carbon cloth surface resulted in current increase of 36% over uncoated carbon cloths. The electrocatalysis experiments using Rh coated carbon cloth resulted in reduction of NO(3)(-) and NO(2)(-) on a timescale of minutes. Nitrite is produced as a product, but is rapidly consumed upon further electrolysis. Field groundwater samples subjected to electrocatalysis experiments, without the addition of NaClO(4)(-) electrolyte, also exhibited removal of NO(3)(-) on a timescale of minutes. Overall, results suggest that at an applied potential of -1.5 V with respect to SCE, Rh coated carbon cloth can reduce NO(3)(-) concentrations in field groundwater samples from 73 to 39 mg/L (16.58 to 8.82 mg/L as N) on a timescale range of 40-60 min. The electrocatalytic reduction process described in this study may prove useful for removing NO(3)(-) and NO(2)(-) from groundwater associated with nonpoint source pollution.

Chemistry of trace elements in coalbed methane product water.

Extraction of methane (natural gas) from coal deposits is facilitated by pumping of aquifer water. Coalbed methane (CBM) product water, produced from pumping ground water, is discharged into associated unlined holding ponds. The objective of this study was to examine the chemistry of trace elements in CBM product water at discharge points and in associated holding ponds across the Powder River Basin, Wyoming. Product water samples from discharge points and associated holding ponds were collected from the Cheyenne River (CHR), Belle Fourche River (BFR), and Little Powder River (LPR) watersheds during the summers of 1999 and 2000. Samples were analyzed for pH, Al (aluminum), As (arsenic), B (boron), Ba (barium), Cr (chromium), Cu (copper), F (fluoride), Fe (iron), Mn (manganese), Mo (molybdenum), Se (selenium), and Zn (zinc). Chemistry of trace element concentrations were modeled with the MINTEQA2 geochemical equilibrium model. Results of this study show that pH of product water for three watersheds increased in holding ponds. For example the pH of CBM product water increased from 7.21 to 8.26 for LPR watershed. Among three watersheds, the CBM product water exhibited relatively less change in trace element concentrations in CHR watershed holding ponds. Concentration of dissolved Al, Fe, As, Se, and F in product water increased in BFR watershed holding ponds. For example, concentration of dissolved Fe increased from 113 to 135 microg/L. Boron, Cu, and Zn concentrations of product water did not change in BFR watershed holding ponds. However, concentration of dissolved Ba, Mn, and Cr in product water decreased in BFR watershed holding ponds. For instance, Ba and Cr concentrations decreased from 445 to 386 microg/L and from 43.6 to 25.1 microg/L, respectively. In the LPR watershed, Al, Fe, As, Se, and F concentrations of product water increased substantially in holding ponds. For example, Fe concentration increased from 192 to 312 microg/L. However, concentration of dissolved Ba, Mn, Cr, and Zn decreased in holding ponds. Geochemical modeling calculations suggested that observed increase of Al and Fe concentrations in holding ponds was due to increase in concentration of Al(OH)(4)(-) and Fe(OH)(4)(-) species in water which were responsible for pH increases. Decreases in Ba, Mn, Cr, and Zn concentrations were attributed to the increase in pH, resulting in precipitates of BaSO(4) (barite), MnCO(3) (rhodochrosite), Cr(OH)(2) (chromium hydroxide), and ZnCO(3) (smithsonite) in pond waters, respectively.

Reaction of CO2 with alkaline solid wastes to reduce contaminant mobility

Abstract The objective of this study was to determine the effects of a CO 2 treatment on the pH and soluble concentrations of inorganic contaminants in alkaline fly ash and spent shale solid wastes. A two-level (low and high), three-variable (moisture, time and pressure) statistical experiment was used to determine optimum CO 2 treatment conditions. Treated and untreated samples were subjected to solubility and X-ray diffraction (XRD) studies. CO 2 treatment conditions of 40 psi of pressure, 20% moisture and 120 h effectively precipitated calcite, and thus lowered the pH and leachable concentrations of certain inorganic contaminants (e.g. Cd, Pb, Zn, Mn, As and Se) in alkaline fly ash and spent shale samples. For instance, ≈64–89% reduction in the leachable concentration of Mn was observed for CO 2 treated samples. Our results suggest that reaction with CO 2 under slightly elevated pressures is an effective means of reducing the soluble concentrations of certain inorganic contaminants in alkaline solid wastes, which should prevent their migration from disposal environments into groundwater.

Method for detecting selenium speciation in groundwater.

To better understand the potential toxicity of Se, it is necessary to know the concentration of different Se ionic species (e.g., SeO 3 2- and SeO 4 2- ). The hydride generation atomic absorption spectrophotometry (HGAAS) method of Se analysis cannot separate Se into individual ionic species. Ion chromatography (IC) can determine SeO 3 2- and SeO 4 2- concentrations simultaneously ; however, common anions, such as sulfate (S0 4 2- ), in groundwater interferes with SeO 3 2- and SeO 4 2- speciation. The purpose of this study was to measure the concentration of ionic SeO 3 2- and SeO 4 2- species in groundwater, thereby determining the chemical speciation of dissolved Se. Three groundwater samples with high concentrations of Mg 2+ and SO 4 2- were used in this study. The ionic SeO 3 2- and SeO 4 2- species in groundwatersamples were selectively adsorbed onto copper oxide (CuO) particles by lowering the pH to 5.5. These ionic species were desorbed from the surface of CuO particles by increasing the pH to 12.5. Subsequently, the concentrations of SeO 3 2- and SeO 4 2- ionic species in solutions were determined with HGAAS and IC. The effect of divalent cations (e.g., Mg 2+ ) on the concentration of SeO 4 2- in aqueous solutions was also evaluated. The dissolved Se concentration in three groundwater samples ranged from 22 to 151 μg/L. The CuO particles extracted 97% of SeO 3 2- from groundwater samples, suggesting that Se(lV) concentrations were dominated by the SeO 3 2- ion. However, CuO particles extracted 80% of SeO 4 2- from groundwater samples. These results suggest that Se(Vl) concentrations consisted of SeO 4 2- and metal SeO 4 2- solution species. The dissolved Mg 2+ in groundwater samples formed a strong neutral ion pair with SeO 4 2- (MgSeO 4 0 ), which was not adsorbed by the CuO particles. Overall chemical speciation of dissolved Se, extracted with CuO particles, suggests that groundwater samples consisted of SeO 3 2- (6-36%), SeO 4 2- (32-65%), organic Se species (14-23%), and neutral ion pairs (9-16%). An important aspect of the proposed method is that CuO can be used in the field to extract both SeO 3 2- and SeO 4 2- ionic species from groundwater samples, and these species could be desorbed from CuO and measured using HGAAS or IC methods, depending upon the concentrations of these species.

Preliminary quantification of metal selenite solubility in aqueous solutions

Abstract Selenium solubilization can be a potential source of environmental contamination in natural systems. Currently no experimental data are available on the solubility of metal selenites in aqueous solutions. The objective of our study was to determine the solubility of Ca, Mg, Mn, and Zn selenites. A dissolution study was conducted for 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 35 and 40 weeks with CaSeO 3 · H 2 O, MgSeO 3 , MnSeO 3 and ZnSeO 3 · H 2 O using different background solutions, including distilled deionized water (DI Water), 0.01 M NaCl, 0.03 M NaCl and 0.02 M Na 2 SeO 3 . For all solids, equilibrium was reached within 40 weeks. As compared to the theoretical values obtained from literature, the experimental p K 0 values for ZnSeO 3 · H 2 O were higher, whereas for MgSeO 3 the determined p K 0 values were lower; theoretical and experimental data for both CaSeO 3 · H 2 O and MnSeO 3 were comparable. A comparison of the p K 0 values also indicated that MgSeO 3 had the highest solubility in DI water, whereas in the three other solutions MnSeO 3 had the maximum solubility. The mean p K 0 values determined for CaSeO 3 · H 2 O, MgSeO 3 , MnSeO 3 and ZnSeO 3 · H 2 O in the above mentioned background solutions were 7.76, 7.56, 7.11, and 7.70, respectively, which indicated that the overall solubility order would be, Mn SeO 3 > MgSeO 3 > ZnSeO 3 · H 2 O > CaSeO 3 · H 2 O. The results of this study are fundamental for modifying existing Se thermodynamic databases and understanding selenite solid-water interactions in natural environments.

Intrinsic properties of cupric oxide nanoparticles enable effective filtration of arsenic from water

The contamination of arsenic in human drinking water supplies is a serious global health concern. Despite multiple years of research, sustainable arsenic treatment technologies have yet to be developed. This study demonstrates the intrinsic abilities of cupric oxide nanoparticles (CuO-NP) towards arsenic adsorption and the development of a point-of-use filter for field application. X-ray diffraction and X-ray photoelectron spectroscopy experiments were used to examine adsorption, desorption, and readsorption of aqueous arsenite and arsenate by CuO-NP. Field experiments were conducted with a point-of-use filter, coupled with real-time arsenic monitoring, to remove arsenic from domestic groundwater samples. The CuO-NP were regenerated by desorbing arsenate via increasing pH above the zero point of charge. Results suggest an effective oxidation of arsenite to arsenate on the surface of CuO-NP. Naturally occurring arsenic was effectively removed by both as-prepared and regenerated CuO-NP in a field demonstration of the point-of-use filter. A sustainable arsenic mitigation model for contaminated water is proposed.

Effect of Flue Gas Treatment on the Solubility and Fractionation of Different Metals in Fly Ash of Powder River Basin Coal

Studies were conducted to examine the effect of flue gas carbon dioxide (CO2) on solubility and availability of different metals in fly ash of Powder River Basin (PRB) coal, Wyoming, USA. Initial fly ash (control) was alkaline and contains large amounts of water-soluble and exchangeable metals. Reaction of flue gas CO2 with alkaline fly ash resulted in the formation of carbonates which minimized the solubility of metals. Results for metal fractionation studies also supported this fact. The present study also suggested that most of the water-soluble and exchangeable metals present in the control (untreated) fly ash samples decreased in the flue gas-treated samples. This may be due to the transfer of the above two forms to more resistant forms like carbonate bound (CBD), oxide bound (OXD), and residual (RS). Geochemical modeling (Visual MINTEQ) of water solubility data suggested that the saturation index (SI) values of dolomite (CaMg(CO3)2) and calcite (CaCO3) were oversaturated, which has potential to mineralize atmospheric CO2 and thereby reduce leaching of toxic metals from fly ash. Results from this study also showed that the reaction of flue gas CO2 with alkaline fly ash not only control the solubility of toxic metals but also form carbonate minerals which have the potential to fix CO2.

Coal Fly Ash Chemistry and Carbon Dioxide Infusion Process to Enhance its Utilization

The increased use of coal in production of electricity is predicted to continue well into the 21st century. Thus, coal burning power plants play a key role in the economic future of the United States. Like any other process, coal combustion process also generates by-products including flue gases (CO2) and solids. Currently, a small portion (20–30%) of the total solids produced is used in cement products and remediation of acidic environments and remainder (80–70%) is disposed of in landfills. In this chapter, a CO2 pressure treatment process to reduce the concentration of extractable trace elements (As, Cd, Pb, and Se) in different alkaline fly ash samples is described. Results suggested that CO2 infusion process effectively precipitated CaCO3 in different alkaline fly ash samples. The precipitation of CaCO3 reduced the concentration of extractable trace elements through adsorption and coprecipitation processes. Different approaches are available to increase the potential use of fly ash. However, the most promising approach is to utilize CO2 and precipitate calcite (CaCO3) in fly ash because it can immobilize contaminants. Additionally, CO2 treated fly ash can be used as a sorbent in remediation of contaminants in other hazardous wastes. However, further research to stabilize alkaline fly ash with flue gas CO2 under actual field conditions is required.

Comparison of ammonium bicarbonate‐DTPA, ammonium carbonate, and ammonium oxalate to assess the availability of molybdenum in mine spoils and soils

Abstract A variety of extractants has been used to assess the availability of molybdenum (Mo) in soils. Most of the extractants have been studied from a deficiency aspect rather than for soils with Mo toxicity, and none of them have been used to extract available Mo from mine spoils. The purpose of this study was to examine the potential of different chemical extractants for assessing the availability of Mo in mine spoils and soils. One mine spoil and three soils were treated with sodium molybdate and then subjected to wetting and drying cycles for two months. These spoil/soils were extracted with ammonium bicarbonate DTPA (AB‐DTPA), ammonium carbonate, and ammonium oxalate solution for available Mo. Crested wheatgrass (Agropyron cristatum) and alfalfa (Medicago sativa) were grown in the spoil/soils in a greenhouse to determine plant uptake of Mo. Additionally, four mine spoils and six soils were extracted and analyzed for available Mo as mentioned above. The results obtained by these three extractants we...