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A novel triethylenetetramine (TEAE) modified chitosan microbeads with multicavity structure encapsulated in alginate backbone (named as HCTA) was fabricated for Cr(VI) removal from aqueous solution. Cr(VI) removal was investigated in batch and column modes. FTIR, SEM-EDS, XRD and XPS, etc. were utilized for characterization of the composites. Multiple mechanisms such as electrostatic interaction, reduction reaction, chelation and cation-exchange involved in the adsorption process. Binary combination of matrix and fillers contributed to highly efficient Cr(VI) removal in a wide pH range (2–10), whereas Na+, Ca2+, Al3+, Cl−, NO 3 − and SO 4 2− had minimal effects on the removal performance. The experimental maximum adsorption capacity was ∼291.3 mg/g at the optimal pH 3.0, much higher than that of alginate beads (∼26.1 mg/g); a three-stage kinetics behavior was observed with ∼50% of the maximum Cr(VI) adsorption capacity within 60 min; the increase of temperature was favorable for adsorption. The experimental data were fitted well to the Freundlich model and the pseudo-second-order model in batch system. The Thomas model was fitted better than Bohart-Adams model with breakthrough curves under different influent flow rate in a column system. Moreover, HCTA beads showed good chemical and mechanical stability for alkali resistance even at high saline conditions. Crucially, excellent reusability of HCTA beads was observed after nine cycles. These results make the novel HCTA beads a promising candidate for Cr(VI) removal in certain practical wastewater. Image 1 • TEAE-modified chitosan with multicavity encapsulated in alginate matrix was prepared. • Highly efficient Cr(VI) removal in a wide pH range. • It exhibits good adaptability and high mechanical and chemical stability. • A better adsorption capacity than most of reported similar adsorbent. [ABSTRACT FROM AUTHOR]

Utilization of coal tailings (CTs) to enable ammonia (NH 3) capture is of interest from pollution control and waste management perspectives. In this work, CTs were surface modified by air oxidation at different temperatures and varying duration to increase the uptake of NH 3. The CTs treated at 300 and 250 °C for 5 h achieved an NH 3 uptake of 52.5 and 45.3 mg g−1, respectively, which was significantly higher than that of the untreated CT (2.1 mg g−1). A linear relationship between NH 3 uptake and concentration of acidic surface functional groups was found (R2 = 0.99). Spectroscopic analysis showed that NH 3 can be retained on the oxidized CT through chemisorption involving carboxylic groups, leading to the formation of amides. Kinetic studies in the temperature range of 200–300 °C revealed an activation energy of 50.2 kJ mol−1 for the formation of acidic surface functional groups on CTs. These comparably mild conditions for the oxidative surface modification make CTs versatile and readily available materials for reducing agricultural NH 3 emissions. [Display omitted] [ABSTRACT FROM AUTHOR]

Ammonium (NH 4 +) and ammonia (NH 3) are notorious hard-to-treat pollutants, leading to serious deterioration of aquatic ecosystems and significant risks to human health. While adsorption is a promising method to tackle this problem, finding suitable adsorbent materials which are abundant, low-cost and efficient remains a constant challenge. Thus, this review summarizes recent development of important adsorbent materials implemented for NH 3 /NH 4 + removal. Advantages and disadvantages of representative adsorbent materials including bentonite, zeolite, clay, biochar, activated carbon, metal organic framework and their modified forms are compared, and the nature of their adsorption processes are discussed in context of adsorption sites, isotherm models (e.g. Langmuir and Freundlich), kinetic equations (e.g. pseudo-first order, pseudo-second order and intra-particle diffusion) and thermodynamic analysis. Future perspective on the utilization of inexpensive lignite is also conferred. Although both conventional and nanostructured materials face challenges regarding economic cost, energy consumption, secondary pollution and adsorption efficiency, these can be tackled by adopting various of advanced options. Current research on adsorption mechanisms forms a solid basis for the design and development of novel adsorbent materials. We speculate that the pursuit of strategies for effective surface modification of natural abundant resources will lead to a bright future of removal processes suited to low NH 3 /NH 4 + concentration conditions. Image 1 [ABSTRACT FROM AUTHOR]

Agricultural processing by-product have been used as the feed stock for effluent treatment to promote the utilization of agricultural waste, the development of green sustainable and construct a green ecological circle nowadays. Based on camellia oleifera shells, attapulgite, and ferric chloride, a novel iron oxide loaded biochar/attapulgite composite (Fe-BC/A) was synthesized via a one-step pyrolysis process and as a low-priced and efficient adsorbent for Cr(VI) removal from aqueous solution. The structure and composition of Fe-BC/A were characterized by SEM-EDS, FT-IR, XRD, and XPS, which confirmed iron oxide (analogous to α-Fe 2 O 3 and β-FeOOH) and attapulgite clay were successfully incorporated with biochar. The maximum adsorption capacity of Cr(VI) by Fe-BC/A was 107 mg/g at pH 2.0, which was much higher than the original biochars (BC: 54.38 mg/g) and biochar/attapulgite composites (BC/A: 81.75 mg/g). The adsorption behavior of Fe-BC/A fitted better with pseudo second-order model and Freundlich model, which indicated that multilayer chemisorption might dominate Cr(VI) adsorption. The thermodynamic analysis of Fe-BC/A represented that removal of Cr(VI) was a spontaneous and endothermic process. Batch experiments results demonstrated that Fe-BC/A had great adsorption capability of Cr(VI) in a broad pH extent of 2.0–10.0, whose most favorable elimination for Cr(VI) at pH of 2.0 and the removal efficiency of Cr(VI) was about 80% at pH = 10 (C 0 = 100 mg/L, 30 °C). Fe-BC/A exhibited a prominent tolerance to the coexisting ions during Cr(VI) removal and only a slight decrease (8.27%) in elimination efficiency after five adsorption-desorption cycles. Mechanism study revealed that electrostatic attraction, reduction, anion exchange, and complexation were involved in the removal of Cr(VI). This study implied the potential practical application of Fe-BC/A in the future Cr(VI) remediation from wastewater. [Display omitted] • Fe-BC/A derived from camellia oleifera shells was synthesized by a simple method. • Efficient removal of Cr(VI) by introducing attapulgite and iron oxide into biochar. • Fe-BC/A showed great adsorption capability of Cr(VI) in a broad pH extent of 2.0–10.0. • Fe-BC/A exhibited a prominent tolerance to the coexisting ions during Cr(VI) removal. [ABSTRACT FROM AUTHOR]