Arsenic adsorption on two types of powdered and beaded coal mine drainage sludge adsorbent

Critical assessment of recent advancements in chitosan-functionalized iron and geopolymer-based adsorbents for the selective removal of arsenic from water

Inorganic arsenic (As), a known carcinogen and major contaminant in drinking water, affects over 140 million people globally, with levels exceeding the World Health Organization's (WHO) guidelines of 10 μg L-1. Developing innovative technologies for effluent handling and decontaminating polluted water is critical. This paper summarizes the fundamental characteristics of chitosan-embedded composites for As adsorption from water. The primary challenge in selectively removing As ions is the presence of phosphate, which is chemically similar to As(V). This study evaluates and summarizes innovative As adsorbents based on chitosan and its composite modifications, focusing on factors influencing their adsorption affinity. The kinetics, isotherms, column models, and thermodynamic aspects of the sorption processes were also explored. Finally, the adsorption process and implications of functionalized chitosan for wastewater treatment were analyzed. There have been minimal developments in water disinfection using metal-biopolymer composites for environmental purposes. This field of study offers numerous research opportunities to expand the use of biopolymer composites as detoxifying materials and to gain deeper insights into the foundations of biopolymer composite adsorbents, which merit further investigation to enhance adsorbent stability.

Simultaneous stabilization/solidification of arsenic in acidic wastewater and tin mine tailings with synthetic multiple solid waste base geopolymer

Stabilization/Solidification (S/S) is considered as a feasible technology for the treatment of arsenic (As) in acidic wastewater (AW) and tin mine tailings (TMTs); however, high cost, high carbon footprint, and strict reaction conditions are the main limitations. Herein, a novel alkali-activated geopolymer material (AAGM) for S/S As was synthesized by combining AW, TMT, gypsum (GP), and metakaolin (MK). At room temperature, an initial As concentration of 3914 mg/L, a NaOH content of 4.98%, and an MK content of 20% decreased the As leaching concentration to 1.55 mg/L (<5 mg/L). The main S/S mechanisms of As included physical encapsulation of C-(A)-S-H and geopolymer structures, ion exchange of ettringite, and formation of Fe-As and Ca-As precipitates. Further studies showed that increasing initial As concentration and MK content facilitated the formation of Ca-As precipitates and C-(A)-S-H gels. The semi-dynamic leaching tests revealed that the leaching mechanism of As was surface wash-off. The effective diffusion coefficients of the samples were less than 10^-13 cm²/s, and the respective leachability indexes were greater than 9, indicating that AAGM was effective in preventing the leaching of As. Therefore, this study provides a green and low cost solution for the synergistic utilization of AW, TMT, GP, and MK.

Development of lab-on-chip biosensor for the detection of toxic heavy metals: A review

Recently, a decrease in water availability and quality has been raised due to rapid industrialization, unsustainable agricultural activities and anthropogenic activities. Heavy metals are considered significant pollutants in the water environment, cause environmental hazards and health effects to humans. For monitoring water contaminants utilized different conventional techniques. Still, they have some drawbacks, such as cost expensive, ecological issues, and processing time, requiring technicians and researchers to operate them effectively. Biosensors have become reasonable devices for screening and identifying environmental contaminants because of their different benefits contrasted with other detecting techniques. This review summarizes the toxic effect of heavy metal and their source, occurrence. A detailed discussion is provided on the heavy metal recognition materials for detecting heavy metals in wastewater. Lab on chip (LOC) is an emerging micro-electrical mechanical system (MEMS) device that intakes liquid and makes it move through the micro-channels, to accomplish fast, cost-effective and profoundly sensitive analysis with significant yield. LOC also provided a discussion on numerous laboratory functions on a single platform. This article attempts to discuss the detection of heavy metals using lab on a chip by suitable recognition materials. Further, the design and fabrication mechanism and their recognition abilities of LOC were also reviewed. The review mainly focuses on the application of LOC biosensors, pros, and cons, and suggests a roadmap towards future development to enhance the practical use in pollutant monitoring.

Efficient removal of arsenic from aqueous solution by continuous adsorption onto iron-coated cork granulates

The search for low-cost technologies for arsenic removal from water is in high demand due to its human toxicity, even at low concentrations. Adsorption can be a cost-effective water treatment technique if applied with inexpensive materials. Arsenic continuous removal by adsorption onto an alternative modified biosorbent, iron-coated cork granulates (ICG), was investigated in this work. Results showed that most experimental parameters of breakthrough curves (BTC) depend on flow rate, bed height, pH, and initial arsenic concentration. The temperature did not significantly affect arsenate removal in continuous mode; however, the adsorption capacity was affected in batch mode. The thermodynamic parameters suggest that the adsorption process is spontaneous and endothermic. The maximum adsorption capacity of ICG for As(V) removal at pH 3 was 4.2 ± 0.3 mg g^-1, calculated by Yan model fit (R² = 0.981), and for As(III) at pH 9 was 1.6 ± 0.2 mg g^-1 (R² = 0.994). ICG were able to treat As(V) from 100 µg L^-1 to under 10 µg L^-1 and 50 µg L^-1 for 895 and 1633 bed volumes, and As(III) for 569 and 861 bed volumes, respectively, both at pH 7. The application of ICG in arsenic oxyanions remediation was found to be effective under various conditions.

Synthesis and Characterization of Porous Chitosan/Saccharomycetes Adsorption Microspheres

Porous chitosan/saccharomycetes adsorption microspheres were successfully prepared by using silica gel as porogen. The morphology of porous chitosan/saccharomycetes microspheres was characterized by scanning electron microscopy, the interaction between molecules was characterized by Fourier transform infrared spectroscopy, and the crystallization property of the microspheres was characterized by X-ray diffraction. The results showed that the adsorption sites of amino and hydroxyl groups had been provided by the porous chitosan/saccharomycetes microspheres for the removal of preservatives, pigments, and other additives in food. The surface roughness of microspheres could be improved by increasing the mass ratio of saccharomycetes. The increase in silica gels could make the microsphere structure more compact. The porous chitosan/saccharomycetes microspheres could be used as adsorbents to adsorb doxycycline in wastewater.

A computational study on the adsorption of arsenic pollutants on graphene-based single-atom iron adsorbents

Integrated gasification combined cycle (IGCC) is a promising clean technology for coal power generation; however, the high volatility and toxicity of arsenic pollutants (As₂, As₄, AsO and AsH₃) released from an IGCC coal plant cause serious damage to human health and the ecological environment. Therefore, highly efficient adsorbents for simultaneous treatment of multiple arsenic pollutants are urgently needed. In this work, the adsorption characteristics and competitive adsorption behaviors of As₂, As₄, AsO, and AsH₃ on four kinds of graphene-based single-atom iron adsorbents (Fe/GA) were systematically investigated through density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. The results suggest that single-vacancy Fe/GA doped with three nitrogen atoms has the largest adsorption ability for As₂, As₄, AsO and AsH₃. The adsorption energies of As₂, AsO and As₄ on Fe/GA depend on both charge transfer and orbital hybridization, while the adsorption energy of AsH₃ is mainly decided by electronic transfer. The adsorption differences of As₂, As₄, AsO and AsH₃ on four Fe/GA adsorbents can be explained through the obvious linear relationship between the adsorption energy and Fermi softness. As₂, As₄, AsO and AsH₃ will compete for adsorption sites when they exist on the same adsorbent surface simultaneously, and the adsorption capacities of AsO and As₂ are relatively stronger. After the competitive adsorption between AsO and As₂, AsO occupies the adsorption site at 300-900 K. This theoretical work suggests that Fe/GA is a promising adsorbent for the simultaneous removal of multiple arsenic pollutants with high adsorption capacity and low cost.

Arsenic adsorption study in acid mine drainage using fixed bed column by novel beaded adsorbent

The downflow fixed-bed column adsorption-desorption of arsenic by the beaded coal mine drainage sludge-Youngdong (BCMDS-YD) adsorbent was experimentally studied. The specific surface area of BCMDS-YD synthesized using inorganic binding was 178 m² g^-1, and the pH_IEP was 5.32. The XRD analysis revealed that it was composed of calcite and schwertmannite. As a result, an increase in the inflow rate resulted in an earlier column exhaustion. The breakthrough curve indicated that a smaller adsorbent particle size and lower influent pH prolonged the column life span. Thomas logistic model was applied to fit the breakthrough curve by linear and nonlinear regression. Under the condition of an influent flow rate of 2.65 mL min^-1 (EBCT 40 min), an influent arsenic average concentration of 0.5-1 mg L^-1, an influent pH of 7.6, an adsorbent mass of 100 g, an adsorbent grain size of 1.40-1.70 mm, and an operating temperature of 25 °C, the equilibrium adsorption capacity reached 4.56 mg g^-1. The mechanism of arsenic adsorption is adsorption and precipitation. As a result of the adsorbent reuse experiment, it was judged that it could be reused with good results in all three cycle experiments. The cost of treating arsenic with the BCMDS-YD adsorbent was 0.145 $ per m^-3. The results of this study show examples of sustainable development concepts in mining drainage, and BCMDS-YD can effectively remove arsenic and other heavy metals from acid mine drainage.

Microbial Community Diversity Dynamics in Acid Mine Drainage and Acid Mine Drainage-Polluted Soils: Implication on Mining Water Irrigation Agricultural Sustainability

Environmental degradation related to mining-generated acid mine drainage (AMD) is a major global concern, contaminating surface and groundwater sources, including agricultural land. In the last two decades, many developing countries are expanding agricultural productivity in mine-impacted soils to meet food demand for their rapidly growing population. Further, the practice of AMD water (treated or untreated) irrigated agriculture is on the increase, particularly in water-stressed nations around the world. For sustainable agricultural production systems, optimal microbial diversity, and functioning is critical for soil health and plant productivity. Thus, this review presents up-to-date knowledge on the microbial structure and functional dynamics of AMD habitats and AMD-impacted agricultural soils. The long-term effects of AMD water such as soil acidification, heavy metals (HM), iron and sulfate pollution, greatly reduces microbial biomass, richness, and diversity, impairing soil health plant growth and productivity, and impacts food safety negatively. Despite these drawbacks, AMD-impacted habitats are unique ecological niches for novel acidophilic, HM, and sulfate-adapted microbial phylotypes that might be beneficial to optimal plant growth and productivity and bioremediation of polluted agricultural soils. This review has also highlighted the impact active and passive treatment technologies on AMD microbial diversity, further extending the discussion on the interrelated microbial diversity, and beneficial functions such as metal bioremediation, acidity neutralization, symbiotic rhizomicrobiome assembly, and plant growth promotion, sulfates/iron reduction, and biogeochemical N and C recycling under AMD-impacted environment. The significance of sulfur-reducing bacteria (SRB), iron-oxidizing bacteria (FeOB), and plant growth promoting rhizobacteria (PGPRs) as key players in many passive and active systems dedicated to bioremediation and microbe-assisted phytoremediation is also elucidated and discussed. Finally, new perspectives on the need for future studies, integrating meta-omics and process engineering on AMD-impacted microbiomes, key to designing and optimizing of robust active and passive bioremediation of AMD-water before application to agricultural production is proposed.