The increasing global demand for safe drinking water has intensified the need for efficient, sustainable, and cost-effective arsenic removal technologies. Among various treatment methods, adsorption remains one of the most viable options, particularly in regions with limited infrastructure and financial resources. In this context, the utilization of industrial by-products such as alum sludge—generated during conventional water treatment processes—offers a promising pathway toward waste valorization and environmental protection.
Alum sludge is rich in amorphous aluminum hydroxide (Al(OH)₃), which exhibits strong affinity for oxyanionic contaminants like arsenate (As(V)) and arsenite (As(III)). However, its application in fixed-bed systems is hindered by poor mechanical stability, leading to bed compaction, channeling, and particle loss. To address these challenges, pelletization using natural binders has been explored. This study focuses on optimizing a pelletized adsorbent composed of alum sludge and bentonite, aiming to balance adsorption performance with structural integrity under continuous flow conditions.
Bentonite, a layered hydrated aluminosilicate clay, was selected as the binder due to its high cation exchange capacity, thermal stability, and ability to form cohesive structures upon hydration. The preparation process involved mixing alum sludge with bentonite at 0.5 wt% and 1.0 wt% ratios based on sludge weight. The mixture was extruded into cylindrical pellets (0.5–1.4 cm length, 0.5 cm diameter), followed by thermal treatment at 400°C for 3 hours in a muffle furnace under ambient air. Post-treatment, pellets exhibited reduced dimensions (0.3–1.0 cm length, 0.2 cm diameter), indicating shrinkage but improved density and strength.
Characterization results revealed that the ASB-0.5 pellet (0.5 wt% bentonite) had a BET surface area of 227.81 m²/g and pore volume of 0.049 cm³/g, significantly lower than the original powder (364.55 m²/g), yet sufficient for effective adsorption. XRF analysis confirmed Al₂O₃ as the dominant component (46%), while SiO₂ content increased due to bentonite addition. FE-SEM images showed a porous internal structure conducive to mass transfer, and post-adsorption imaging indicated no structural degradation or surface alteration, confirming the material’s chemical and physical stability.
Batch studies demonstrated that ASB-0.5 achieved a maximum adsorption capacity of 22.2 mg As/g, representing about 40% of the powdered form. While this reduction is attributed to pore blockage by bentonite, it was offset by substantial gains in mechanical strength. Compressive strength rose from undetectable levels in raw sludge to 3.086 N/mm² for ASB-0.5—a 3.6-fold improvement. Mass loss during agitation dropped to just 10%, compared to 36.4% in previous molasses-based pellets, proving the effectiveness of bentonite as a robust, non-degradable binder.
Adsorption kinetics followed pseudo-second-order behavior (r² = 0.97), with equilibrium reached after 28 hours. Despite slower initial rates due to larger particle size and diffusion limitations, the system maintained consistent performance over extended periods. Isotherm modeling fit best with the Freundlich model (r² = 0.99), suggesting heterogeneous adsorption sites and favorable interaction between arsenic and aluminum oxide surfaces.
Critical to real-world application is performance in column systems. Continuous flow experiments were conducted using glass columns (1.5 cm inner diameter), packed with ASB-0.5, powdered alum sludge (ABA), and commercial GFH. A constant flow rate of 0.2 mL/min was applied, and effluent samples were analyzed via ICP-OES. Results showed that ASB-0.5 achieved a breakthrough volume of 477 BV—slightly higher than GFH (451 BV) and ABA (456 BV)—indicating superior longevity.VAV1 Antibody custom synthesis Moreover, no clogging or channeling was observed, unlike the powdered forms, which suffered from uneven flow distribution and premature failure.VEGFR3 Antibody web
The calculated lifetime of ASB-0.PMID:34414469 5 was 27.4 days, surpassing GFH (26.3 days) and ABA (26.7 days). Each kilogram of ASB-0.5 could treat up to 900 liters of arsenic-contaminated water (initial concentration: 100 mg/L) before exceeding the WHO standard of 10 ppb. Furthermore, the pellet retained its shape throughout testing, eliminating the need for backwashing or frequent media replacement.
Competitive anion effects were evaluated using common groundwater ions: Cl⁻, SO₄²⁻, NO₃⁻, HCO₃⁻, SiO₃²⁻, and PO₄³⁻. Phosphate showed the strongest inhibitory effect due to site competition, but its typical low concentration in natural waters minimizes practical impact. Other anions had negligible influence.
In conclusion, the pelletized alum sludge-bentonite adsorbent presents a highly effective, durable, and economically viable solution for arsenic removal in continuous flow systems. It successfully overcomes the inherent weaknesses of powdered adsorbents while maintaining competitive adsorption performance. By transforming waste into functional material, this approach supports circular economy principles and offers a scalable technology for addressing arsenic pollution in vulnerable communities worldwide.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com