Adsorptive removal of Cr(III) from aqueous solution using tripolyphosphate cross-linked chitosan beads

Use of (modified) natural adsorbents for arsenic remediation: A review

Arsenic (As) is a ubiquitous element found in the atmosphere, soils and rocks, natural waters and organisms. It is one of the most toxic elements and has been classified as a human carcinogen (group I). Arsenic contamination in the groundwater has been observed in >70 countries, like Bangladesh, India, West Bengal, Myanmar, Pakistan, Vietnam, Nepal, Cambodia, United States and China. About 200 million people are being exposed to excessive As through consumption of contaminated drinking water. Therefore, developing affordable and efficient techniques to remove As from drinking water is critical to protect human health. The currently available technologies include coagulation-flocculation, adsorption, ion exchange, electrochemical conversion and membrane technologies. However, most of the aforementioned treatment techniques require high initial and maintenance costs, and skilled manpower on top of that. Nowadays, adsorption has been accepted as a suitable removal technology, particularly for developing regions, because of its simple operation, potential for regeneration, and little toxic sludge generation. Processes based on the use of natural, locally available adsorbents are considered to be more accessible for developing countries, have a lower investment cost and a lower environmental impact (CO₂ emission). To increase their performance, these materials may be chemically modified. Hence, this review paper presents progress of adsorption technologies for remediation of As contaminated water using chemically modified natural materials.

Removal of Arsenic (V) from Aqueous Solutions Using Chitosan-Red Scoria and Chitosan-Pumice Blends

In different regions across the globe, elevated arsenic contents in the groundwater constitute a major health problem. In this work, a biopolymer chitosan has been blended with volcanic rocks (red scoria and pumice) for arsenic (V) removal. The effect of three blending ratios of chitosan and volcanic rocks (1:2, 1:5 and 1:10) on arsenic removal has been studied. The optimal blending ratio was 1:5 (chitosan: volcanic rocks) with maximum adsorption capacity of 0.72 mg/g and 0.71 mg/g for chitosan: red scoria (Ch–Rs) and chitosan: pumice (Ch–Pu), respectively. The experimental adsorption data fitted well a Langmuir isotherm (R² > 0.99) and followed pseudo-second-order kinetics. The high stability of the materials and their high arsenic (V) removal efficiency (~93%) in a wide pH range (4 to 10) are useful for real field applications. Moreover, the blends could be regenerated using 0.05 M NaOH and used for several cycles without losing their original arsenic removal efficiency. The results of the study demonstrate that chitosan-volcanic rock blends should be further explored as a potential sustainable solution for removal of arsenic (V) from water.