Red mud-chitosan microspheres for removal of coexistent anions of environmental significance from water bodies

Bauxite residue (red mud) treatment: Current situation and promising solution

Bauxite residue, an industrial solid waste generated during alumina production, with over 80 % of bauxite residue worldwide being accumulated around alumina plants, which occupying a significant amount of land resources and posing a threat to the natural environment in the surrounding areas. This paper reviews recent advances in extracting valuable resources from bauxite residue, and its applications in building materials, environmental adsorbents, energy storage materials, and soil alkalinization. It also highlighted the main problem existing in these researches, which is the inability of the existing single processes to achieve the comprehensive utilization of various types of bauxite residue or maximize the utilization of bauxite residue components, resulting in a low comprehensive utilization rate and insignificant absorption effects of bauxite residue. To address these issues, we proposed a strategy of classifying and utilizing bauxite residue based on its components and establishing a multi-industry application system, involving sectors such as steel and building materials. This collaborative approach aims to handle various types of bauxite residue more effectively. Additionally, we suggest selecting suitable treatment methods based on the specific characteristics of bauxite residue and implementing measures to promote its comprehensive and large-scale utilization.

Amputation of Remazol brilliant blue dye on crosslinked chitosan hydrogel: Statistical treatment and experimental evaluation

The primary aim of this research is to comprehensively assess the applicability of chitosan biopolymer towards water treatment application and to enhance its adsorption capacity towards Remazol brilliant blue R-19 dye. This has been achieved through physical modification to obtain the material in hydrogel form and chemical modification by crosslinking it with barbituric acid. The characterization of the resulting Chitosan-barbituric acid hydrogel (CBH) was carried out using various analytical techniques such as SEM-EDX, FT-IR, TGA-DTA, XRD, and BET. CBH was employed as the adsorbent to eliminate R-19 dye from aqueous media. Utilizing response surface methodology (RSM), the parameters were fine-tuned, leading to the achievement of more than a 95% removal for R-19 dye. The adsorption behavior closely adhered to the Langmuir isotherm and pseudo-second-order kinetics. An interesting observation indicated that the rise in temperature leads to rise in adsorption capacity of CBH. The maximum adsorption capacities evaluated at 301.15 K, 313.15 K, 318.15 K, and 323.15 K were 566.6 mg g-1, 624.7 mg g-1, 671.3 mg g-1, and 713.5 mg g-1 respectively, in accordance with the Langmuir isotherm model. Examining the thermodynamics of the adsorption process revealed its spontaneous nature (ΔG = -21.14 to -27.09 kJ mol-1) across the entire temperature range. Furthermore, the assessment of the isosteric heat of adsorption (ΔHads) was conducted using the Clausius-Clapeyron equation, with results indicating an increase in ΔHads from 1.85 to 2.16 kJ mol-1 with temperature rise from 301.15 K to 323.15 K due to augmented surface loading. This suggested the existence of lateral interactions between the adsorbed dye molecules. The potential of adsorbent for regeneration was investigated, demonstrating the ability to reuse the material. Sustainability parameter calculated for synthesis process reflected a notably low E-factor value of 0.32 demonstrated the synthesis is environment friendly.

Chitin extraction from crab shells and synthesis of chitin @metakaolin composite for efficient amputation of Cr (VI) ions

The present research study combines chitin from shrimp waste with the oxide-rich metakaolin. Metakaolin is a blend of mixed oxides rich in silica and alumina with good adsorbent properties. The chitin@metakaolin (CHt@M.K.) composite was synthesized and characterized using FTIR, SEM, TGA, XRD and XPS techniques. Cr(VI) removal studies were compared for chitin and CHt@M.K. through adsorption. It was found that the adsorption capacity of CHt@M.K. is 278.88 mg/g, almost double that of chitin, at pH 5.0 in just 120 min of adsorption. Isotherm models like Langmuir, Freundlich, Temkin and Dubinin-Radushkevich were investigated to comprehend the adsorption process. It was revealed that Langmuir adsorption isotherm is most suitable to elucidate Cr(VI) adsorption on CHt@M.K. The adsorption kinetics indicate that pseudo first order was followed, indicating that the physisorption was the process that limited the sorption process rate. The positive enthalpy change (20.23 kJ/mol) and positive entropy change (0.083 kJ/mol K) showed that the adsorption process was endothermic and more random at the solid-liquid interface. The negative free energy change over entire temperature range was an indicator of spontaneity of the process. Apart from all these, the non-covalent interactions between Cr(VI) and composite were explained by quantum calculations based models.

Recent advances in removal of inorganic anions from water by chitosan-based composites: A comprehensive review

Chitosan is a modified natural carbohydrate polymer that has been found in the exoskeletons of crustaceans (e.g., lobsters, shrimps, krill, barnacles, crayfish, etc.), mollusks (octopus, oysters, squids, snails), algae (diatoms, brown algae, green algae), insects (silkworms, beetles, scorpions), and the cell walls of fungi (such as Ascomycetes, Basidiomycetes, and Phycomycetes; for example, Aspergillus niger and Penicillium notatum). However, it is mostly acquired from marine crustaceans such as shrimp shells. Chitosan-based composites often present superior chemical, physical, and mechanical properties compared to single chitosan by incorporating the benefits of both counterparts in the nanocomposites. The tunable surface chemistry, abundant surface-active sites, facilitation synthesize and functionalization, good recyclability, and economic viability make the chitosan-based materials potential adsorbents for effective and fast removal of a broad range of inorganic anions. This article reviews the different types of inorganic anions and their effects on the environment and human health. The development of the chitosan-based composites synthesis, the various parameters like initial concentration, pH, adsorbent dosage, temperature, the mechanism of adsorption, and regeneration of adsorbents are discussed in detail. Finally, the prospects and technical challenges are emphasized to improve the performance of chitosan-based composites in actual applications on a pilot or industrial scale.