Removal of As (V) from the aqueous solution by a modified granular ferric hydroxide adsorbent

https://doi.org/10.1016/j.scitotenv.2019.135947Get rights and content

Highlights

  • Novel granular adsorbents were prepared from iron ore for As (V) removal.

  • The adsorbent was characterized in detail (morphology, chemical characteristics).

  • The influences are pH, initial concentration, contact time, dose and temperature.

  • As (V) removal mechanism by granular ferric hydroxide adsorbent was proposed.

  • The adsorbent can be applied for drinking water treatment at large scale.

Abstract

A novel adsorbent was prepared in granular form from iron (III) hydroxide and other additives to remove arsenate (As (V)) from aqueous solution. Adsorption of As (V) onto the adsorbent in batch experiments was analyzed to understand the adsorption mechanism, affecting factors, and adsorption isotherms. The optimal working conditions for the developed adsorbent were at pH 3, 30 °C and 50 g/L. The adsorption of arsenate onto the adsorbent occurred rapidly in the first 10 min and reached equilibrium in 2 h. The Langmuir isotherm was found to be best fitted the adsorption. The pre- and post-adsorption adsorbents were characterized by SEM, BET, FTIR, XRD, and Zeta potential techniques. Experimental results clearly demonstrated the potential impact of elemental composition, crystallinity, surface morphology, and other physico-chemical properties of the adsorbent on the adsorption performance variety. The experimental results with the pilot scale treatment system revealed that the adsorbent can be applied successfully and lead to a very efficient drinking water treatment system, at a competitive cost compared to the water market in Hanoi, Vietnam.

Introduction

The presence of inorganic forms of arsenic in water poses a serious threat to human health (Choong et al., 2007). Exposure to arsenic can cause serious diseases such as skin discoloration, cancer of the skin, kidney and lungs, blood vessel diseases, high blood pressure, and reproductive disorders (Thanawatpoontawee et al., 2016; Siddiqui and Chaudhry, 2017). Due to its toxicity and occurrence, the World Health Organization (WHO) and Vietnam Ministry of Health have set the maximum arsenic contaminant level of 10 μg/L for drinking water (World Health Organization, 2011; National technical regulation on drinking water quality, 2009). Studies indicated that the arsenic occurrence in many areas in Vietnam such as Red river delta and Mekong river delta are higher than the regulation levels (Van Thinh et al., 2018; Postma et al., 2017; Van Geen et al., 2013). Removal of arsenic to provide safe drinking water has been investigated by many earlier studies employing a range of techniques such as coagulation and flocculation, ion exchange, precipitation, membrane filtration, ozone oxidation, biological treatment, electrochemical treatment, and adsorption (Choong et al., 2007; Thanawatpoontawee et al., 2016; Jacobson and Maohong, 2019). Among them, adsorption has several advantages over other methods, due to the low investment cost, ease of operation and efficiency in the removal of in-organic pollutants including arsenic (Tran et al., 2015). Activated carbon is an effective adsorbent for removing micropollutants from drinking water and wastewater because of its high surface area, porosity and physico-chemical characteristics. However, its use is limited due to high costs and low selectivity (Balsamo et al., 2010). Recently, powdered iron oxides or hydroxides have been reported to be effective in removing arsenic from water (Zhang et al., 2003; Wu et al., 2011; Pham et al., 2016). Nevertheless, they are difficult to apply in large-scale scenarios because of their complex operational requirements. Utilization of low-cost and local availability of materials presents a potential source of adsorbents, and solves part of the drinking water and wastewater problems. In Vietnam, there is a diversity of natural minerals and industrial wastes such as iron ore, kaolinite, bentonite, plating sludge, red mud and aluminum hydroxide, which are low cost and are locally available. Although use of iron-based materials such as iron hydroxide for removing arsenic has been studied since a long time ago (Driehaus et al., 1998), this study aims to develop a novel adsorbent from materials that are locally available in Vietnam. Furthermore, the removal mechanism of arsenic from the adsorbent are not fully understand and lack of economic assessment reports of application for real water treatment in developing countries.

To achieve the objectives, this research will focus on: (i) development of a novel granular iron hydroxide adsorbent to remove arsenic for water treatment; (ii) evaluation of the factors which effects on adsorption capacity of this granular adsorbent; (iii) proposing driving forces for arsenic removal from water by the adsorbent; and (iv) use of the adsorbent in a pilot scale treatment system and determine the toxicants' removal ability, and economic efficiency.

Section snippets

Adsorbent and arsenic solution preparation

Iron (III) hydroxide was prepared from iron ore (Cao Bang Mirex Company, Vietnam) as the following reactions: Fe2O3 + 6 HCl → 2 FeCl3 + 3 H2O and FeCl3 + 3 NaOH → Fe(OH)3 + 3 NaCl. It was then filtered, dried for 12 h, heated at 105 °C in 4 h, then smashed and sieved with d < 0.074 mm. Other additives such as kaolinite, bentonite and aluminum hydroxide can form the special structure of the adsorbent, which has many pore on the granular ferric hydroxide material. The adsorbent preparation

Adsorbent characterization

The photo and SEM images in Fig. 2A, B indicate that the surface of the adsorbent includes many pores and walls which might favored the adsorption of arsenic on its surface. XRD spectrum demonstrated the existence of SiO2, hematite and maghemite on the surface of IH (Fig. 2C).

The BET surface area results confirmed that the surface area of the powdered adsorbent was 22.69 m2/g while after arsenic adsorption it fell slightly to 22.03 m2/g (Table 2). This could be explained by an amount of arsenic

Conclusion

The experimental results confirmed that iron hydroxide-based adsorbent IH (in granular form) did effectively remove arsenate from water. The material has an average BET surface area, i.e. 22.69 m2/g. The three main oxides on the surface of the adsorbents were SiO2, Fe2O3 and γ-Fe2O3. Functional groups of IH which are possibly responsible for the adsorption of arsenate onto the material include Fesingle bondOH and FeO stretches. The value of pHPZC involving the surface charge of IH was 1.5. The predominant

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors acknowledge the support of the Faculty of Environmental Sciences, VNU University of Science, Vietnam National University, Hanoi. The authors are grateful for the financial support from the project entitled “Development of a pilot scale technology model for treating industrial waste sludge which is rich in heavy metals towards resources recovery, energy saving – KC.08.18/16-20”. The authors are very grateful for the research collaboration between Faculty of Environmental Sciences,

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