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.

Field experiments were conducted to assess the influence of plant growth and amendment addition on phytostabilisation of copper (Cu), lead (Pb), manganese (Mn) and zinc (Zn) along highway soil in southwest British Columbia, Canada. The plant species tested were Lolium perenne L (perennial rye grass), Festuca rubra L. (creeping red fescue) and Poa pratensis L. (Kentucky blue grass) and the amendments, lime and phosphate. The treatment efficiencies were assessed during different seasons as a completely randomized factorial experiment in split plot design. The research tasks involved: (1) quantifying the seasonal extent of metal accumulation in soil and assessing the seasonal impact on metal speciation for different soil amendments and plant species; (2) determining seasonal accumulation differences between sampling periods in plant parts; and (3) assessing the influence of root–soil interactions on metal dynamics. The amendments decreased the exchangeable fraction and plant uptake of all four metals. The lowest mobile fractions (exchangeable and carbonate bound) were found in soils growing Festuca for Cu, Lolium for Mn and a Lolium/Poa/Festuca combination for Pb and Zn. Metal accumulation and metal dynamics in the rhizosphere soil are compared with those of the bulk soil. The final outcome was the development of a remediation strategy for all four metals involving suitable plants and amendments and incorporating seasonal and rhizosphere influences.

Rare earth mineral based adsorbent viz. lanthanum oxide was investigated for potential application in defluoridation of drinking water for isolated and rural communities. Results of batch experiments indicated about 90% removal in 30 min from a 4 mg L−1 synthetic fluoride solution. The effects of various parameters like contact time, pH, initial concentration, and sorbent dose on sorption efficiency were investigated. Adsorption efficiency was dependent on initial fluoride concentration and the sorption process followed BET model. Variation of pH up to 9.5 has insignificant effect on sorption and beyond a pH of 9.5, the effect was drastic. Among anions investigated, carbonates exhibited high detrimental effect on fluoride adsorption while anions like bicarbonates, chlorides, and sulfates did not seriously affect the process. Adsorbent showed negligible desorption of fluoride in distilled water. Alum was more effective regenerant than HCl and NaOH. Results of cyclic regeneration with alum indicated that the sorbent could be regenerated for ten cycles without significant loss of sorption capacity. Studies with upflow fixed-bed continuous flow columns indicated the usefulness of sorbent for fluoride removal in continuous flow process.

The objective of this study was to investigate the effects of adding different rates of diethylenetriamine pentaacetate (DTPA) at different concentrations (0, 0.5, 1, and 5 mmol kg−1) and ethylenediamine disuccinate (EDDS) at 0, 5, 7.5, and 10 mmol kg−1 on the capacity of Brussels sprouts plants to take up Se from soils contaminated with 0, 5, 10, and 15 mg kg−1 NaSeO4, under a greenhouse conditions. Results indicated that the application of DTPA and EDDS to Se-contaminated soils significantly affect plant Se concentration, Se uptake, and dry matter yield of plants. Se concentration in the plant leaves, stems, and roots increased with increase in DTPA and EDDS application doses, but total Se uptake increased from 0 to 1.0 and 7.5 mmol kg−1 DTPA and EDDS application doses, respectively, and decreased after those levels due to toxic Se concentration for plant. Most plant available fractions and the carbonate, metal oxide, and organic matter-bound fractions increased linearly with Se application. At all DTPA and EDDS application rates, the Se concentrations in the leaves were about two to three times higher than those in the roots and about three to four times higher than those in the stems. This study suggests that the above-ground organs like leaf and shoots of Brussels sprouts can effectively be used in the removal of Se from soils contaminated with Se. Under the conditions in this experiment, Brussels sprouts were capable of removing 0.9–1.8 mg Se pot−1 when harvested at maturity without any chelating agent take into consideration one growing season per year. Based on the data of present experiment, it would be necessary to approximately 57–67 growing seasons without EDDS and EDTA to remove all total Se from polluted soil. Selenium removal can be further increased 12- to 20-fold with 7.5 mmol kg−1 EDDS and 1.0 mmol kg−1 DTPA application, respectively.

Reclamation of land disturbed due to mining in arid and semiarid environments occurs across the globe. Large-scale surface mines provide unique opportunities to examine the reclamation process across a landscape. The objectives of this research were to (1) measure infiltration rates in reclaimed surface coal mines and (2) determine the effects of soil properties on ground cover on infiltration rates of surface coal mines. In this study, reclaimed land 10–15 and 20–25 years old, and native reference site (undisturbed) were investigated at two large surface coal mines in Wyoming, USA. Infiltration rates were measured using double-ring infiltrometer method. The soil properties including bulk density, pH, carbonate content, organic carbon content, aggregate stability, electrical conductivity, and soil texture were analyzed using standard methods. The ground cover was estimated visually. Statistical analysis was conducted to determine if any correlations between infiltration rate and soil properties and ground cover exist. Results suggest that at Mine 1, infiltration rates on reclaimed land were found to be significantly higher in the 20–25-year-old reclamation than the 10–15-year-old reclamation and the native site. At Mine 2, the native site had significantly higher infiltration than 20–25-year-old reclamation, which in turn had significantly higher infiltration rates than the 10–15-year-old reclaimed site. Along with infiltration, soil characteristics were examined. Overall, the findings of this study suggest soil texture and plant cover play an important role in controlling infiltration rates in reclaimed surface coal mines.