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Coupling of Speciation and Transport Models
Published in Herbert E. Allen, E. Michael Perdue, David S. Brown, Metals in Groundwater, 2020
Charles J. Hostetler, Robert L. Erikson
Figure 7 shows the soil concentration of cadmium after ten years for the combined solubility and adsorption run. The filled symbols are the results of the CTM simulation, and the open symbols are the results calculated from the ADR equation, using a Kd of two. The presence of cadmium in the soil as a discrete solid phase (in this case otavite) and the sharpness of the calcite dissolution front leads to a large increase in the predicted cadmium concentration at the pH front. This is not predicted by the ADR equation. As cadmium concentrations of 3 μg/g in soil are detectable by standard analytical means, predictions of this sort could be validated in the field.
Removal of Inorganic Contaminants
Published in Samuel D. Faust, Osman M. Aly, Chemistry of Water Treatment, 2018
The MCL for cadmium in drinking water is 0.005 mg/L (see Chapter 1). Surface water contents of Cd in North America2 ranged from 21 to 130 μg/L. It is not especially widespread from natural geologic sources, but may occur in substantial concentrations due to the discharge of wastewaters, especially plating wastes. The aqueous chemistry of cadmium is, for the most part, dominated by Cd2+, CdCO3(s) (otavite), and Cd(OH)2(S).2, 71 The appropriate reactions are: () Cd2++CO32-=CdCO3(s)(otavite)ΔG°REX=−15.25kcal/mollogKs=11.18 () Cd2++2OH−=Cd(OH)2(s)ΔG°REX=−19.62kcal/mollogKs=14.4(aged) () logKs=13.7(fresh)
Quality and hydrogeochemistry appraisal for groundwater in Tenth of Ramadan Area, Egypt
Published in Water Science, 2020
Lubna A. Ibrahim, Eman R. Nofal
In general, elevated concentrations of TDS, aluminum, cadmium, iron, lead, calcium, sodium, chloride, sulfate, nitrate and fluoride were observed in groundwater at site 1 and site 3, according to Egyptian National Guideline for Drinking Water (2007). Spatial water quality variation exhibited that 17 elements showed significant (P < .05) spatial distribution. The investigation discovers in the light of model calculations that Fe2+, Na+, Ca2+, Mg2+, K+, Cl−, SO42-, NO3−, F− and HCO3− are highly soluble and consequently will be bioavailable at the pH ranges of the studied wells. The outcome reveals that these free ions at such level (site 1 and site 3) would be accessible for uptake by plants, animals and humans. It is additionally profoundly conceivable that such conditions may have a negative health impact since their concentrations exceed the permissible limits for drinking purposes. The groundwater samples are super-saturated (SI>0), as for goethite, hematite, ferrihydrite, gibbsite, aragonite, boehmite, diaspore, hercynite, maghemite, magnesioferrite, calcite, dolomite & K-jarosite and undersaturated with regarding to gypsum, fluorite, halite (NaCl), Cd(OH)2, Pb(OH)2, otavite and cerussite. The outcomes of the saturation index exhibited that dissolution and precipitation are influencing the groundwater composition in the study area. The process water-rock interaction (evaporation, dissolution, precipitation, ion exchange and reverse ion exchange) is impacting the aquifer quality of the study area. In view of the results of this study, proper design and implementation of wells are highly recommended to reduce water treatment costs and considering water treatment technologies as desalinization.
Bioremediation potential and primary mechanism of Sporosarcina pasteurii for cadmium (Cd) and lead (Pb) in contaminated tailings
Published in Chemistry and Ecology, 2023
The XRD spectra were acquired to identify the main precipitates from biomineralization for Cd and Pb (Figure 7). The results showed that a minute quantity of Cd/Pb precipitates formed for mineralisation was likely covered by an enormous amount of SiO2 and minerals containing Ca, Al, Fe, and Mg in tailings, which explained the failure to detect Cd/Pb minerals (Figure 7(a)). To prevent the interference from other metal ions in tailings, the precipitates from the S. pasteurii-treated modulated Cd/Pb mixture were used to determine mineral crystals in presence of both these two ions (Figure 7(b)). The peak area indicated that the biominerals were dominated by cerussite and hydrocessite, supplemented by cadmium carbonate and cadmium hydroxide. It was determined by the fact that the concentration of Pb was much higher than that of Cd in the modulated Cd/Pb mixture. Therefore, at the coexistence of two metal ions, the main precipitates induced by S. pasteurii were metal carbonate precipitates and co-precipitates, such as PbCO3, CdCO3, and Pb3(CO3)2(OH)3, etc. Similarly, in the single metal solution, where the UPB secretion (urease) reacted with urea to release CO32- and OH-, the metals minerals otavite and cadmium hydroxide (Cd(OH)2) were detected in full detail (Figure 7(c)). The main minerals from precipitates containing only Pb identified were cerussite, hydrocerussite, lead hydroxide, and additional massicot (Figure 7(d)). The increasing pH could accelerate the precipitation process of those complexed trace elements in the hydrolysis of urea into ammonia. Therefore, it was not difficult to interpret that there were many hydroxyl and carbonate precipitates and co-precipitates to immobilise Cd and Pb in S. pasteurii-treated tailings.
Cadmium removal by bioclastic granules (Lithothamnium calcareum): batch and fixed-bed column systems sorption studies
Published in Environmental Technology, 2018
Diego Macedo Veneu, Claudio Luiz Schneider, Marisa Bezerra de Mello Monte, Osvaldo Galvão Caldas Cunha, Lídia Yokoyama
In the sorption tests carried out in batch, it can be concluded that at pH > 5, the percentages of Cd(II) removal were the most significant (> 97.7%), this is due to the formation of CdCO3 that presents a higher stability and lower solubility than CaCO3, thus favoring its precipitation on the BG surface. From the initial concentration of 0.5 g L−1 of BG, removal results higher than 94% have been achieved, showing a high affinity between BG and Cd(II) ions. With the sorption data obtained at the different Cd(II) concentrations (from 5 to 400 mg L−1), it was possible to observe that the Langmuir isotherm model showed a better correlation coefficient (R2 = 0.965) with qmax = 188.7 mg g−1 much higher than many natural materials based on calcium carbonate. The sorption process was very fast, obtaining removals higher than 98.5% in the first 20 minutes. The uptake data fitted well to the kinetic model of pseudo-first-order (R2 = 0.999), calculated qeq of 49.28 mg g−1 and k1 of 0.199 min−1. The rupture time of the fixed-bed column was 48 h, presenting a qtotal of 12,089.9 mg, been this values well above those obtained by some authors in studies conducted with materials based on calcium carbonate. The rupture curve data fitted well for the Thomas and Yoon–Nelson models, presenting the values of kTh and qo corresponding to 0.895 mL h−1 mg−1 and 124.4 mg g−1 and KYN and τ corresponding to 0.090 h−1 and 82.12 h. In the results of XRD after the sorption process, we detected the presence of otavite (CdCO3) that presents the trigonal crystalline system, the same as the calcite phase. In the SEM, it was possible to observe the presence of a monolayer formed from the BG surface, showing that probably the predominant sorption mechanism is the nucleation and growth of otavite crystals.