Many anionic pollutants (e.g., fluoride, nitrate and nitrite, bromate, phosphate, arsenate and arsenite, selenate and selenite, perchlorate) have been detected in surface and groundwater in different parts of the world and strict measures are being taken to minimize their concentrations and to control their mobility in aqueous media. Mineral surfaces, in general, have shown enhanced uptake of many anionic pollutants. Various phases of aluminum (Al) oxides, hydroxides and oxyhydroxide are increasingly being employed as adsorbents for the detoxification of water and wastewater contaminated with anionic pollutants. Understanding the structural properties and morphology of adsorbents is important in order to gain knowledge about the governing mechanism behind the adsorption of anions by these adsorbents. The adsorption ability of aluminum oxides, hydroxides and oxyhydroxide depends on several key factors including properties of the adsorbent (surface area, pore size, pH_pzc, porosity) and that of the adsorbates. This paper provides an overview of the physical and chemical properties of various aluminum oxides, hydroxides and oxyhydroxides and their application in water and wastewater treatment with the focus on the removal of anionic pollutants. Furthermore, the performance of these minerals and that of the synthetically prepared hybrid adsorbents (containing Al-minerals) for the adsorption of various anions has been reviewed with an emphasis on the behavior of adsorbent-water interface in presence of the anionic pollutants.

A number of inorganic anions (e.g., nitrate, fluoride, bromate, phosphate, and perchlorate) have been reported in alarming concentrations in numerous drinking water sources around the world. Their presence even in very low concentrations may cause serious environmental and health related problems. Due to the presence and significance of iron minerals in the natural aquatic environment and increasing application of iron in water treatment, the knowledge of the structure of iron and iron minerals and their interactions with aquatic pollutants, especially inorganic anions in water are of great importance. Iron minerals have been known since long as potential adsorbents for the removal of inorganic anions from aqueous phase. The chemistry of iron and iron minerals reactions in water is complex. The adsorption ability of iron and iron minerals towards inorganic anions is influenced by several factors such as, surface characteristics of the adsorbent (surface area, density, pore volume, porosity, pore size distribution, pH(pzo) purity), pH of the solution, and ionic strength. Furthermore, the physico-chemical properties of inorganic anions (pore size, ionic radius, bulk diffusion coefficient) also significantly influence the adsorption process. The aim of this paper is to provide an overview of the properties of iron and iron minerals and their reactivity with some important inorganic anionic contaminants present in water. It also summarizes the usage of iron and iron minerals in water treatment technology. (C) 2013 Elsevier B.V. All rights reserved.

In the era of urbanization, industrialization and population growth, groundwater and drinking water sources are getting adversely polluted due to the addition of different toxic contaminants including inorganic anionic pollutants. The inorganic anions are of serious concern due to their adverse health effects on humans, even when present at very low concentrations in water. Adsorption process is an attractive method for the removal of anions as compared to other water treatment technologies in terms of cost, simplicity of design and operation. In this study, granular ferric hydroxide (GFH) and nano-Al₂O₃ were tested for the removal of fluoride, perchlorate and nitrate anions from aqueous solutions. Different experimental parameters (viz. pH, agitation time, adsorbate concentration, temperature, competing anions) have been studied to optimize the adsorption process. The maximum adsorption capacity of 7.0 mg g^-1 (at pH 6.0-7.0) and 20.0 mg g^-1 (at pH 6.0-6.5) for fluoride and perchlorate, respectively was achieved using GFH at 25 ^oC. Adsorption kinetics of fluoride by GFH was favorably explained with pseudo-first-order, while perchlorate adsorption kinetics followed pseudo-second-order model. The Langmuir model explained the adsorption isotherms of fluoride and perchlorate by GFH. The Raman spectroscopy results revealed that perchlorate was adsorbed through electrostatic attraction between perchlorate and positively charged GFH surface sites. The adsorption efficiencies achieved by nano-Al₂O₃ for nitrate and fluoride were 4.0 mg g^-1 (at pH ~4.4) and 14.0 mg g^-1 (at pH ~6.15), respectively at 25 ^oC. Kinetics and isotherms of fluoride and nitrate by nano-Al₂O₃ were well-explained by pseudo-second-order model and Langmuir isotherm model, respectively. The FTIR and EDX results reveal that aluminum-fluoro complexes are formed due to the interaction between fluoride and nano-Al₂O₃ moieties. In all the cases, the most influencing anions were the ones that compete for similar binding sites on the adsorbent surface. Results from this study will be helpful in demonstrating potential utility of the tested adsorbents for the removal of different anions from water and provide an insight into the adsorbent-adsorbate (anions) interactions in the aqueous media.

The present study was conducted to evaluate the feasibility of nano-alumina (Al(2)O(3)) for fluoride adsorption from aqueous solutions. The nature and morphology of pure and fluoride-sorbed nano-alumina were characterized by SEM with EDX, XRD, and FTIR analysis. Batch adsorption studies were performed as a function of contact time, initial fluoride concentration, temperature, pH and influence of competing anions. Fluoride sorption kinetics was well fitted by pseudo-second-order model. The maximum sorption capacity of nano-alumina for fluoride removal was found to be 14.0 mg g(-1) at 25 degrees C. Maximum fluoride removal occurred at pH 6.15. The fluoride sorption has been well explained using Langmuir isotherm model. Fluoride sorption was mainly influenced by the presence of PO(4)(3-), SO(4)(2-) and CO(3)(2-) ions.

Fluoride contamination in drinking water due to natural and anthropogenic activities has been recognized as one of the major problems worldwide imposing a serious threat to human health. Among several treatment technologies applied for fluoride removal, adsorption process has been explored widely and offers satisfactory results especially with mineral-based and/or surface modified adsorbents. In this review, an extensive list of various adsorbents from literature has been compiled and their adsorption capacities under various conditions (pH, initial fluoride concentration, temperature, contact time, adsorbent surface charge, etc.) for fluoride removal as available in the literature are presented along with highlighting and discussing the key advancement on the preparation of novel adsorbents tested so far for fluoride removal. It is evident from the literature survey that various adsorbents have shown good potential for the removal of fluoride. However, still there is a need to find out the practical utility of such developed adsorbents on a commercial scale, leading to the improvement of pollution control.

The present research evaluates the efficacy of granular ferric hydroxide (GFH) for perchlorate removal from aqueous solutions. Laboratory scale experiments were conducted to investigate the influence of various experimental parameters such as contact time, initial perchlorate concentration, temperature, pH and competing anions on perchlorate removal by GFH. Results demonstrated that perchlorate uptake rate was rapid and maximum adsorption was completed within first 30 min and equilibrium was achieved within 60 min. Pseudo-second-order model favorably explains the sorption mechanism of perchlorate on to GFH. The maximum sorption capacity of GFH for perchlorate was ca. 20.0 mg g(-1) at pH 6.0-6.5 at room temperature (25 degrees C). The optimum perchlorate removal was observed between pH range of 3-7. The Raman spectroscopy results revealed that perchlorate was adsorbed on GFH through electrostatic attraction between perchlorate and positively charged surface sites. Results from this study demonstrated potential utility of GFH that could be developed into a viable technology for perchlorate removal from water.

This research was undertaken to evaluate the feasibility of granular ferric hydroxide (GFH) for fluoride removal from aqueous solutions, Batch experiments were performed to study the influence of various experimental parameters such as contact time (1 min-24 h), initial fluoride concentration (1-100 mg L(-1)), temperature (10 and 2S degrees C), pH (3-12) and the presence of competing anions on the adsorption of fluoride on GFH. Kinetic data revealed that the uptake rate of fluoride was rapid in the beginning and 95% adsorption was completed within 10 min and equilibrium was achieved within 60 min. The sorption process was well explained with pseudo-first-order and pore diffusion models. The maximum adsorption capacity of GFH for fluoride removal was 7.0 mg g(-1). The adsorption was found to be an endothermic process and data conform to Langmuir model. The optimum fluoride removal was observed between pH ranges of 4-8. The fluoride adsorption was decreased in the presence of phosphate followed by carbonate and sulphate. Results from this study demonstrated potential utility of GFH that could be developed into a viable technology for fluoride removal from drinking water.

The present study was undertaken to evaluate the adsorption potential of Citrus limonum (lemon) peel as an adsorbent for the removal of two anionic dyes, Methyl orange (MO) and Congo red (CR) from aqueous solutions. The adsorption was studied as a function of contact time, initial concentration, and temperature by batch method. The adsorption capacities of lemon peel adsorbent for dyes were found 50.3 and 34.5 mg/g for MO and CR, respectively. The equilibrium adsorption data was well described by the Langmuir model. Three simplified kinetic models viz. pseudo-first-order, pseudo-second-order, and Weber and Morris intraparticle diffusion model were tested to describe the adsorption process. Kinetic parameters, rate constants, equilibrium sorption capacities, and related correlation coefficients for each kinetic model were determined. It was found that the present system of dyes adsorption on lemon peel adsorbent could be described more favorably by the pseudo-first-order kinetic model. The results of the present study reveal that lemon peel adsorbent can be fruitfully utilized as an inexpensive adsorbent for dyes removal from effluents.