Preparation and Characterization of Homopolymer Polyacrylonitrile-Based Fibrous Sorbents for Arsenic Removal

Abstract

This research investigated the modification of homopolymer polyacrylonitrile (PAN) fibers for use as an adsorbent for removing arsenic from drinking water. Fibers were chemically modified and cross-linked using combinations of hydrazine hydrate and sodium hydroxide (NaOH) before being loaded with ferric hydroxide using two different iron loading procedures. Effects of reagent concentrations and reaction times on degree of chemical modification and fiber properties were investigated using Fourier transform infrared spectroscopy and ion-exchange measurements. Arsenate adsorption was a function of both the iron loading and the properties of the underlying fiber. For fibers treated with only a single reagent, both Fe 3 + and arsenate adsorption could be understood in terms of ion-exchange properties of the fiber surfaces. However, for fibers treated with both hydrazine and NaOH, the ion-exchange properties of the surface could not explain the Fe 3 + and arsenate adsorption behavior. The best arsenate removal performance was obtained using the simplest pretreatment procedure of soaking in 10% NaOH at 95°C for 90 min, followed by precipitation coating of ferric hydroxide. This simple preparation procedure involves only two commonly available and inexpensive reagents and can be carried out without any specialized equipment. This suggests that adsorbents based on inexpensive homopolymer PAN fabric may be produced in developing areas of the world where commercial products may not be available.

Understanding Regeneration of Arsenate-Loaded Ferric Hydroxide-Based Adsorbents

“…Fiban As5 and Fiban A1 media were obtained from the National Academy of Science (Minsk, Belarus), and ArsenX np was obtained from the Purolite Company (Bala Cynwyd, PA). An adsorbent prepared in our laboratory from homopolymer polyacrylonitrile (PAN) obtained from Heading Filter Material Co., Ltd., (Zhejiang, China) was also investigated (Chaudhary and Farrell, 2014). The Fiban As5 material consists of a nonwoven PAN felt that has been treated with hydrazine and N-N 0 -dimethyl-1,3-propanediamine and contains 4.2 meq/g WBA-exchange groups consisting of ternary amines (Soldatov, 2008;Nesteronok and Soldatov, 2012).…”

“…The Fiban A1 medium was loaded with ferric hydroxide by soaking in 6% ferric chloride solution for 60 min and then raising the pH to 8.0 by NaOH addition (Lin and SenGupta, 2009). The PANFe medium was prepared from homopolymer PAN needlepunched felt fabric with a weight of 500 g/m 2 and a fiber diameter of 15 lm (Chaudhary and Farrell, 2014). The PANFe adsorbent was loaded with ferric hydroxide without any pretreatment of the fiber and thereby contains no ionexchange functionality.…”

“…Although the chemical compositions of the SBA sites on the Fiban A1 medium are all the same, not all the sites have the same relative affinity for AsO 4 3 -versus OH -. Previous investigators have found that the spacing of the ion-exchange sites can affect the selectivity of SBA-exchange media (Clifford and Weber, 1983). The positioning of the SBA sites within the media depends on the tacticity and orientation of the polymer chains.…”

“…In locations where two or three SBA sites are in close proximity, an AsO 4 3 -anion can interact with more than one amine site and there may be a much stronger preference for a multivalent over a monovalent anion. In contrast, in locations where SBA sites are spaced so that an AsO 4 3 -can interact with only a single site, monovalent ions may be preferred over multivalent ions (Clifford and Weber, 1983).…”

An overview of synthetic modification of nitrile group in polymers and applications

“…Adsorption of Arsenate (As 3+ ) from drinking water using ferric hydroxide loaded amidrazone modified PAN fibers was reported by Chaudhary and Farrell . Here fibers were chemically modified and cross‐linked using combinations of hydrazine hydrate and sodium hydroxide (NaOH) before being loaded with ferric hydroxide.…”