Cadmium Capture Research Articles

β-Lactoglobulin Enhances Clay and Activated Carbon Binding and Protection Properties for Cadmium and Lead.

The removal of heavy metals from wastewater remains a challenge due to the limitations of current remediation methods. This study aims to develop multicomponent composites as inexpensive and environmentally friendly sorbents with enhanced capture of cadmium (Cd) and lead (Pb). The composites are based on calcium montmorillonite (CM) and activated carbon (AC) because of their proven effectiveness as sorbents for diverse toxins in environmental settings. In this study, we used a combination of computational and experimental methods to delineate that β-lactoglobulin enhances CM and AC binding and protection properties for Cd and Pb. Modeling and molecular dynamics simulations investigated the formation of material systems formed by CM and AC in complex with β-lactoglobulin and predicted their capacity to bind heavy metal ions at neutral pH conditions. Our simulations suggest that the enhanced binding properties of the material systems are attributed to the presence of several binding pockets formed by β-lactoglobulin for the two heavy metal ions. At neutral pH conditions, divalent Cd and Pb shared comparable binding propensities in all material systems, with the former being consistently higher than the latter. To validate the interactions depicted in simulations, two ecotoxicological models (L. minor and H. vulgaris) were exposed to Cd, Pb, and a mixture of the two. The inclusion of CM-lactoglobulin (β-lactoglobulin amended CM) and AC-lactoglobulin (β-lactoglobulin amended AC) at 0.05-0.2% efficiently and dose-dependently reduced the severe toxicity of metals and increased the growth parameters. This high efficacy of protection shown in the ecotoxicological models may result from the numerous possible interaction pockets of the β-lactoglobulin-amended materials depicted in simulations. The ecotoxicological models support the agreement with computations. This study serves as a proof of concept on how computations in tandem with experiments can be used in the design of multicomponent clay- and carbon-based sorbent amended systems with augmented functionalities for particular toxins.

The Capture of Cadmium from Solution during the Replacement of Calcite by Apatite.

The capture of cadmium (Cd) from phosphate-containing solutions during the replacement of CaCO3 by phosphate phases such as hydroxylapatite (HAP) and tricalcium phosphate (TCP) has been studied under high and low temperature and pressure conditions using atomic force microscopy, scanning electron microscopy equipped with an X-ray spectrometer and a backscattered electron detector, Raman spectroscopy, and microprobe analysis. Starting with cubes of Carrara Marble (polycrystalline calcite) and single crystals of calcite, a new solid phosphate phase was observed to incorporate Cd from solution, formed under different pressure and temperature conditions tested. Results showed that Cd precipitated in a new phase on the surface of all samples tested. In Carrara Marble, pseudomorphic replacement of CaCO3 is restricted possibly due to kinetic limitation caused by the adsorption of Cd complexes formed in solution at reactive surface sites and the variation of fluid composition inside the sample. However, on the sample surface, this kinetic limitation is less influential, so the new phase could incorporate higher amounts of Cd faster. Furthermore, this reaction at room temperature was found to have similar and/or better Cd-uptake efficiency as HAP and CaCO3 in pure Cd solution through the precipitation of Cd-containing phosphate crystals on the sample surface. Both reactions were able to capture Cd in the precipitating phase structure and could provide a mechanism for simultaneous Cd and phosphate removal from solutions contaminated with both, in industrial or natural settings.

Dual Benefits of Hydrogel Remediation of Cadmium-Contaminated Water or Soil and Promotion of Vegetable Growth under Cadmium Stress.

This study aims to solve the problem of cadmium heavy metal ion pollution caused by the abuse of chemical fertilizers and activities such as mining, which pose a serious threat to the plant growth environment. We successfully synthesized DMAPAA (N-(3-(Dimethyl amino) propyl) acrylamide)/DMAPAAQ (N, N-Dimethyl amino propyl acrylamide, methyl chloride quaternary) hydrogels via free radical polymerization. Subsequently, we conducted experiments on this hydrogel for growing vegetables under cadmium stress conditions in aqueous solutions and soil. The cadmium capture capacity of DMAPAA/DMAPAAQ hydrogels under different cadmium ion concentrations and pH values was evaluated by using inductively coupled plasma optical emission spectrometry (ICP). The research results show that under the condition of pH = 7.3, the cadmium capture capacity of DMAPAA/DMAPAAQ hydrogels is the greatest. We used the Langmuir model to fit the adsorption data, and the correlation coefficient was as high as 0.96, indicating that the model fits well. The application of the hydrogels promoted the growth of vegetables in soil under cadmium stress conditions. The results showed that when the added amount of hydrogel was 4%, the dry weight of the vegetables was the largest. In addition, when the added amount of cadmium was 500 mg/kg and the added amount of hydrogel was 4%, the absorption of cadmium by the vegetables decreased to an undetectable level. In summary, the hydrogel successfully synthesized in this study can be effectively used to immobilize cadmium ions in soil while positively promoting the growth and yield of vegetables. This achievement has practical significance for solving the problem of heavy metal ion pollution.

Experimental and theoretical studies of cadmium adsorption over Fe2O3 sorbent in incineration flue gas

Iron oxide (Fe2O3) has been used as an effective sorbent to remove various heavy metals due to its large adsorption capacity and low cost. The cadmium capture capability of Fe2O3 sorbent was investigated in the simulated flue gas at the temperatures of 700–1100 °C. Fe2O3 sorbent exhibited much better Cd adsorption capability than SiO2 and Al2O3 sorbents. The largest Cd adsorption capacity of Fe2O3 sorbent was 86.7 mg/g at 700 °C. The XPS analysis demonstrated that Fe3+ might partially participate in the cadmium adsorption process. A large quantity of CdO was generated and adsorbed on the Fe2O3 surface. The density functional theory (DFT) calculations were used to determine the active sites and the involved mechanism of different cadmium species adsorption over Fe2O3 sorbent. Cd, CdCl2, and CdO can be stably adsorbed on the Fe2O3 surface with the adsorption energies of −40.64 kJ/mol, −237.42 kJ/mol, and −375.03 kJ/mol, respectively. The results illustrate that the Fe atoms are the essential active sites for cadmium species adsorption on Fe2O3 surface. The orbital hybridization between cadmium atom and Fe site suggests that the strong interaction occurs during Cd adsorption process. Both physisorption and chemisorption mechanisms were responsible for the cadmium capture by Fe2O3 sorbent.

Accumulators for the Capture of Heavy Metals in Thermal Conversion Systems

A clay ceramic with organic additives (biomass and biochar) was investigated for the development of highly porous accumulators to capture heavy metals in thermal conversion systems. The structure was characterized using X-ray pair distribution function analysis, differential scanning calorimetry, and scanning electron microscopy. It was found that the organic additives transformed into porosity during firing. The morphology of the pores also corresponded to the morphology of the organic additives. Hence, the clay ceramic with a 15-wt% addition of biochar had a porosity of 46 vol% with 20-μm interconnected pores after firing. The resulting accumulator was found to capture cadmium (a model for heavy metals with high volatility) via condensation of the cadmium vapor as 2-μm beads in the pores. The cadmium capture efficiency reached up to 57% using a 15-wt% addition of biochar. Furthermore, cadmium was captured at higher temperatures than the condensation temperature in the atmosphere. This means that heavy metals may be captured before they condense in fly ash to promote the recycling of this material.

The Capture of Cadmium by Reactive Polysulfides Attenuates Cadmium-Induced Adaptive Responses and Hepatotoxicity.

Cadmium (Cd) is an environmental electrophile that modifies protein nucleophiles, thereby modulating cellular signaling and toxicity. While reactive persulfides/polysulfides exhibit relatively high nucleophilic properties, their roles in the altered gene expression and toxicity caused by Cd remain unclear. Exposing primary mouse hepatocytes to Cd caused heat shock protein 70 (HSP70) and metallothionein (MT)-I/II to be upregulated and cytotoxicity to occur. These effects were blocked in the presence of polysulfide sodium tetrasulfide (Na2S4). Electrospray ionization mass spectrometry analysis indicated that cadmium sulfide (CdS) and cadmium thiosulfate (CdS2O3) were produced when Cd reacted with Na2S4. Authentic CdS did not cause cellular signaling responses to be activated or hepatotoxic effects, while CdS2O3 had effects similar to those of Cd. HSP70 and MT-I/II upregulation and hepatotoxicity caused by exposure to Cd were significantly enhanced by the deletion of cystathionine γ-lyase (CSE), which catalyzes the formation of reactive persulfides/polysulfides. Deleting CSE also exacerbated Cd-mediated liver injury, whereas little hepatic damage was found when CdS or Na2S4 along with Cd was administered. Overall, the results suggest that the persulfide/polysulfide-mediated formation of sulfur adducts of Cd such as CdS rather than CdS2O3 is, at least in part, involved in decreasing the level of Cd-mediated activation of cellular signaling and toxicity.

Cadmium-Mediated Activation of the HSP90/HSF1 Pathway Regulated by Reactive Persulfides/Polysulfides.

Cadmium is an environmental electrophile that modifies reactive thiols in proteins, indicating that this heavy metal may modulate redox-signal transduction pathways. The current consensus is that reactive persulfides and polysulfides produced by cystathionine γ-lyase (CSE) and cystathionine β-synthase are highly nucleophilic and thus cadmium may be captured by these reactive sulfur species. It has previously been found that electrophile-mediated covalent modifications of the heat shock protein (HSP) are involved in the activation of heat shock factor 1 (HSF1) pathway. The effects of cadmium on the activation of HSP/HSF1 pathway were investigated in this study. Exposure of bovine aortic endothelial cells to cadmium resulted in modification of HSP90 and HSF1 activation, thereby up-regulating the downstream protein HSP70. The siRNA-mediated knockdown of HSF1 enhanced the cytotoxicity induced by cadmium, suggesting that the HSP90/HSF1 pathway contributes to protection against cadmium toxicity. The knockdown of CSE and/or cystathionine β-synthase decreased the levels of reactive sulfur species in the cells and increased the degree of HSP70 induction and cytotoxicity caused by exposure to cadmium. Overexpression of CSE diminished cadmium-mediated up-regulation of HSP70 and cytotoxicity. These results suggest that cadmium activates HSF1 by modifying HSP90 and that reactive sulfur species regulate the redox signal transduction pathway presumably via capture of cadmium, resulting in protection against cadmium toxicity under toxic conditions.

Anhydride Functional Nanocoatings for Heavy Metal Cadmium Capture and Release

Pulsed plasmachemical deposited poly(maleic anhydride) nanolayers display high efficiency for the capture of toxic cadmium ions from aqueous solution (down to the low parts per billion range). Subsequent release of the isolated heavy metal species and host media regeneration is accomplished by rinsing in weak acid solution.

Cadmium Biosoption by Immobilized Dead yeast cells From Bioethanol Industries

Dead yeast cells are an abundant residue of the Brazilian ethanol industry and the industries still don’t have a proper or desirable destiny for all these cells, which means tons of vitamins and proteins that have not a major end. In the other hand, heavy metal residues are a problem, especially for leather industry, where Brazil is also a great producer. In this work, dead yeast cells were used to evaluate cadmium biosorption samples. Results have shown that dried dead yeast cells at 20 % (W/V) immobilized in Na-alginate beads 0.5 % can be an efficient alternative for the capture of cadmium. The average biosorption rate was 122.10 mg Cd/ g of dry biomass in comparison to the control using only the Na-alginate beads 0.5 % where the biosorption rate achieved 57.29 mg Cd/g of dry biomass. This research opens wide opportunities to allies two major residues created in Brazilian industries with a noble end for the industries it selves as for the environment.

Cadmium adsorption by coal combustion ashes-based sorbents—Relationship between sorbent properties and adsorption capacity

A very interesting possibility of coal combustion ashes reutilization is their use as adsorbent materials, that can also take advantage from proper beneficiation techniques. In this work, adsorption of cadmium from aqueous solutions was taken into consideration, with the emphasis on the intertwining among waste properties, beneficiation treatments, properties of the beneficiated materials and adsorption capacity. The characterization of three solid materials used as cadmium sorbents (as-received ash, ash sieved through a 25μm-size sieve and demineralized ash) was carried out by chemical analysis, infrared spectroscopy, laser granulometry and mercury porosimetry. Cadmium adsorption thermodynamic and kinetic tests were conducted at room temperature, and test solutions were analyzed by atomic absorption spectrophotometry. Maximum specific adsorption capacities resulted in the range 0.5–4.3mgg−1. Different existing models were critically considered to find out an interpretation of the controlling mechanism for adsorption kinetics. In particular, it was observed that for lower surface coverage the adsorption rate is governed by a linear driving force while, once surface coverage becomes significant, mechanisms such as the intraparticle micropore diffusion may come into play. Moreover, it was shown that both external fluid-to-particle mass transfer and macropore diffusion hardly affect the adsorption process, which was instead regulated by intraparticle micropore diffusion: characteristic times for this process ranged from 4.1 to 6.1d, and were fully consistent with the experimentally observed equilibrium times. Results were discussed in terms of the relationship among properties of beneficiated materials and cadmium adsorption capacity. Results shed light on interesting correlations among solid properties, cadmium capture rate and maximum cadmium uptake.

Implementation of a prototype slow positron beam at the NC State University PULSTAR reactor

A prototype beam system was designed and tested to verify the potential of utilizing the North Carolina State University PULSTAR reactor in generating slow positrons. An annealed tungsten converter/moderator was placed at the end of beam tube ♯6 near the PULSTAR core and surrounded by 0.5-mm-thick cadmium cover. Fission and cadmium capture γ-rays were used to drive pair production reactions in the tungsten. The positrons emitted from tungsten were electrostatically focused and guided using a magnetic solenoid until they reached the exit of the biological shield. An aluminum plate that was placed near the exit served as an annihilation target for the positrons. A coincidence counting system was set up to measure the true coincidence rate of the 511 keV annihilation photons that are produced once the slow positrons strike the aluminum target. The data demonstrated the production and control of slow positrons at a rate greater than 10 7e +/s.

In-furnace capture of cadmium and other semi-volatile metals by sorbents

An 18 kW, cylindrical (inside diameter = 15-cm), 6-m high, laminar, downflow furnace was used to investigate the mechanisms governing reactive scavenging of cadmium vapors from combustion environments, by hydrated lime and kaolinite powder sorbents. Two major physical mechanisms dominate the reaction rate and sorbent utilization during the capture of semi-volatile metal by kaolinite, temperature-activated eutectic-melting-enhanced capture and excessive-melt deactivation, initiated at a higher temperature than the enhancement. However, cadmium forms higher temperature eutectics than other semi-volatile metals such as lead and sodium, which have a transition to a deactivating melt below 1100 °C. The network modifier responsible for the reaction enhancement is the metal/sorbent reaction product itself, which forms a eutectic with the remaining, unreacted sorbent. Global rate models were developed to describe the reaction of kaolinite with lead, sodium, and cadmium metal vapors. The following reaction scheme was valid for all three metal vapors, Na/Pb/Cd: Na 2 O / PbO / CdO + 1 2 ( Al 2 O 3 · 2 SiO 2 ) ⇒ P Na / Pb / Cd . Followed by the substrate (melting) deactivation step for Na and Pb, but not for Cd: P Na / Pb + 1 2 ( Al 2 O 3 · 2 SiO 2 ) ⇒ D + P Na / Pb . Eutectic-melting enhancement of cadmium capture by both kaolinite and hydrated lime was initiated between 1160 and 1280 °C. Cadmium is more effectively captured at higher temperatures (i.e., ∼1300 °C) than other semi-volatile metals, such as lead and sodium, and requires even higher temperatures to cause sorbent deactivation by excessive melting. Unlike cadmium, lead and sodium were poorly scavenged by hydrated lime.

Capture of Potassium and Cadmium by Kaolin in Oxidizing and Reducing Atmospheres

Nutrient elements including alkali metals in biomass ash need to be returned to the forest by ash recycling. It is, however, difficult to recycle the total biomass ash due to the high concentrations of heavy metals in some ash fractions. During fluidized bed combustion of biomass, alkali metals tend to attach on bed particles or deposit on heat transfer surfaces, causing bed agglomeration, slagging, and fouling problems, while heavy metals are found enriched in the fly ash. Therefore, it is important to control both alkali and heavy metals during combustion of biomass. In this study, the competition between potassium and cadmium adsorption on kaolin was investigated experimentally in a fixed bed reactor equipped with an alkali detector. The experiments were made at 850 °C under both oxidizing and reducing conditions, which are relevant to fluidized bed combustion of biomass. The oxidizing gas was air, while the reducing gas was composed of 80% N2, 10% CO, and 10% CO2. Fine aerosols of droplets containing the metals in water were produced from their aqueous solutions by means of an atomizer and subsequently vaporized in the reactor. Atomic absorption spectrometry (AAS) and X-ray powder diffraction (XRD) techniques were used for quantitative and qualitative analyses of the products. The results indicate that potassium is captured by kaolin in both oxidizing and reducing atmospheres. Kaolin captures cadmium in air, but not under reducing conditions. In addition, reducing conditions appear to promote potassium adsorption on kaolin. The copresence of potassium and cadmium compounds in the gas phase promotes the capture of both metals by kaolin. This promotion was more pronounced for potassium than for cadmium, indicating a preference of kaolin for potassium capture over cadmium capture. In air, the total amount of potassium captured by kaolin increased when cadmium was added, but the water-soluble fraction decreased slightly. Moreover, kaolin captures KCl slightly more effectively than KOH in air, but less effectively than KOH under reducing conditions.

High-temperature interactions between multiple-metals and kaolinite

High-temperature combustion flue gases provided the environments for this investigation of multiple-metals interactions with dispersed kaolinite. Whereas previous research was restricted to interactions of single-metals with kaolinite powders, this work focuses on understanding how kaolinite transformations induced by reaction with one metal species can affect the mechanisms of interaction with other metal species. Experiments were performed in an 18 kW downflow furnace, by doping combinations of semi-volatile metals through a natural gas flame, and injecting supermicron sized powder kaolinite sorbent into the post flame. An aerosol size fractionation method was used to quantify the fraction of metal captured. It was found that the melt-associated restructuring of the meta-kaolinite crystal, caused by eutectics formed with lead and sodium reaction products (self-enhancing for lead and sodium capture), enhances the capture of cadmium by kaolinite at 1160°C. Cadmium reaction products by themselves fail to initiate a self-enhancing eutectic-melt at this temperature, because cadmium forms a higher temperature eutectic with the meta-kaolinite crystal than does lead or sodium. In fact, at temperatures in the range 1000°C to 1300°C, cadmium enhances the capture of lead and sodium by slowing down the deactivating excessive-melt driven by the lead or sodium/sorbent eutectic at these temperatures. Hence, total metal capture is enhanced in this temperature range for the Cd/Pb and Cd/Na systems by the formation of an optimum eutectic-melt, whereby significant melt-enhancement is induced without sorbent deactivation. Lead and sodium reaction products form similar high-temperature eutectics with kaolinite. However, sodium capture dominates over lead capture with a slightly higher reaction rate than lead, thus achieving capture before the most significant sorbent deactivation occurs. Sodium also dominates by effectively displacing lead previously captured on sorbent sites. These observations are quantified using models that extend those developed for single-metal capture to multiple-metal situations.

In situ remediation of groundwater contaminated by heavy- and transition-metal ions by selective ion-exchange methods.

Laboratory studies were conducted to investigate the feasibility of using ion-exchange resins in permeable reactive barriers (PRBs) for the remediation of groundwater contaminated by heavy and transition metals. Ion-exchange resins represent an essentially neglected class of materials which may, in addition to iron, activated carbon, and zeolites, prove effective for use in PRBs. Four resins were considered: two commercially available resins, Duolite GT-73 (Rohm and Haas) and Amberlite IRC-748 (Rohm and Haas), and two solvent-impregnated resins (SIRs). The SIRs were prepared from Amberlite IRA-96 (Rohm and Haas) and two different thiophosphoric extractants. All four resins are able to reduce cadmium, lead, and copper concentrations from 1000 microg/L (typical for contaminated groundwaters) to below 5 microg/L. Significantly, all of the resins are effective for the capture of cadmium, copper, and lead, even in the presence of CaCl2 and clay. Because of their high hydraulic conductivity, the use of these resins in clusters of wells, as an alternative to continuous walls, is considered in the design of effective PRBs. Numerical solution of the groundwater flow equations shows that, depending on the well configuration, most (or all) of the contaminated groundwater can pass through the resins. These results demonstrate the possibility of using selective ion-exchange resins as an effective, active material in PRBs for in situ groundwater remediation.

Quantitative Analysis of High Temperature Toxic Metal Sorption Rates Using Aerosol Fractionation

The airborne emission of toxic metals, such as lead, arsenic, and cadmium, from coal-fired boilers and incinerators is a major problem. These metals, which are considered to be semivolatile, are vaporized in the flame and subsequently form submicron particles. Since submicron particles are difficult to remove, one strategy to prevent emission is to inhibit ultra-fine particle formation within the combustor. Recent work has demonstrated that the sorbents such as kaolinite and lime are able to capture semivolatile metal vapors at high temperatures, thus preventing nucleation and condensation at lower temperatures. However, to develop practical scale technology, the rate of metal sorption by sorbents must be quantified. In this paper, an aerosol size fractionation approach is proposed to determine the extent of metal vapor-sorbent interactions above the metal dew point. The applicability of this methodology is illustrated by determining the rate of capture of cadmium by powdered, kaolinite sorbent at high co...

Study of the Adsorption of CdCl2 Vapor on Various Minerals Using a Drop Tube Furnace

Most of these studies were performed with fixed bed or thermogravimetric apparatus, and it is often difficult to correlate the results of these experiments with incineration flue gas conditions. To study more precisely the reaction between heavy metal vapor and suspended particles, the GRE laboratory has developed a drop tube furnace. With this experimental setup, it was possible to quantify the adsorption of cadmium chloride on different sorbents in conditions representative of incinerators; a dilute stream of particles was in contact with a counter current flow of metal vapors at high temperature during a few seconds. Leaching was done to quantify the physisorbed and chemisorbed fractions of the metal. Silica, alumina, alumina-silica, and calcium oxide were used, and the influence of sorbent surface area, gas temperature, and metal vapor concentration was studied. Alumina and calcium oxide were found to be more effective for cadmium capture. The leachable fraction of cadmium on each sorbent appears to be very low. This is in favor of a chemisorption mechanism. Results were correlated with Freundilch isotherms to get characteristic values of vapor chemisorption on these sorbents.

Capture of volatile hazardous metals using a bed of kaolinite

One of the promising technologies for reducing metals emission from the waste thermal process is the capture of vapor-phase metals through the use of solid sorbents. This study investigated the use of natural kaolinite for the removal of several volatile metals. The capture of cadmium and lead using a packed bed with porous kaolinite of the size range 300-400 Μm was effective. The capturing efficiency increased as the bed temperature increased. The ratio of the sorption reaction rate to the diffusion rate varied on the 10-2 order of magnitude. This suggests that the resistance of the diffusion within the pores of kaolinite particles is not significant in the selection of sorbent particle size for practice. The capturing mechanism for cadmium chloride is different from that for lead chloride. Cadmium can be reactively scavenged by CdO-Al2O3-2SiO2 as well as metakaolinite, suggesting that a unit mole of metakaolinite can ultimately capture two moles of cadmium.

Iron and Cadmium Capture Gamma-Ray Photofission Measurements

Photofission measurements have been made in {sup 238}U, {sup 232}Th, and {sup 237}Np in iron and cadmium capture gamma-ray spectra in cylindrical neutron-driven gamma-ray sources in the thermal column of the National Bureau of Standards (NBS) Reactor. The gamma-ray source strength was measured with neutron activation foils and by direct counting of activations produced in the metal cylinders. Photofission measurements were made with NBS miniature fission chambers. The integral photofission cross sections were compared with differential measurements by integrating the capture gamma-ray spectra with measured cross-section shapes. The integral cross sections measured in the capture gamma-ray fields are lower than the cross sections calculated from measured differential data.