Investigations on arsenic(V) removal by modified calcined bauxite

Abstract

The present study suggests a solution to the real life problem of arsenic poisoning of potable ground water by examining the use of calcined bauxite, a locally available adsorbent in a modified form, for arsenic(V) scavenging. This adsorbent (modified calcined bauxite, MCB) exhibited excellent As(V) removal (99–100%) over a wide range of pH ∼ 2–8 in batch studies. In the neutral pH range (pH ∼ 7), the intensity of adsorption increased from 0.099 to 1.37 mg g −1 corresponding to initial As(V) concentrations of 0.5–8 mg l −1 with a dose of 5 g l −1 within 3 h. The sorption kinetics was found to follow the pseudo-second order model. The Langmuir, Freundlich and Dubinin–Radushkevich models were tried to represent the equilibrium data of As(V) adsorption. The removal of As(V) can be best modeled using Langmuir isotherm which renders the maximum adsorption capacity as 1.566 mg g −1. The sorption process was almost unaffected by temperature variations. During sorption, no appreciable ionic effects except from SO 4 2− and EDTA complex were observed from the background ions Ca 2+, Fe 3+, Cl −, NO 3 −, PO 4 3− and F −. The most distinguishing characteristic was the pH of the effluent within the drinking water range of 6–7.5. The column study results show that at a sorbent bed depth of 10 cm and feed flow rate of 8 ml min −1, the MCB media was capable of treating 8.16 l (260 bed volumes) of As(V) spiked water ( C 0 = 2 mg l −1) before breakthrough. The values of adsorption rate coefficient ( K) and adsorption capacity coefficient ( N) are calculated using Logit method of column design and were found to be 0.2467 l mg −1 h −1 and 865.85 mg l −1, respectively. The XRD data analysis describes chemical combinations of the sorption mechanism. The consistency in arsenic sorption over a wide pH range, availability and adaptability in the local environment, excellent sorption potential, least interference from most of the anions, negligible temperature effects and quality of the treated water makes it an ideal choice for arsenic removal.