Synthesis Of Nanoscale Zero Valent Iron Composites For Removal Of Arsenic

Arsenic is extremly harmful pollution to human health. Inorganic arsenic in water can be present in nonionic trivalent arsenite [As(III)] complex and ionic pentavalent arsenate [As(V)] oxyanions. Among various methods for removal of arsenic ions, nanoscaled zero valent iron (nZVI) particles have been proved as an efficiency adsorbent, because of its higher specific area and higher active energy. However, the nZVI adsorbents with small dimensions and high activity are impossible to recycle through common means, resulting in secondary pollution to the environment. To circumvent these disadvantages, carbonizing fiber and chitosan were chosen as base materials to synthesis nZVI composite materials for removal of arsenic in waste water. The details are presented as follows.1. nZVI/carbon fiber composites (ICs) were produced by supported nZVI particles on the carbon fiber prepared through high-temperature annealing cotton for the removal of arsenic ions. The thermogravimetric analysis and infrared analysis of carbonized fiber revealed that the carbonization of cotton started at 400 ℃ and the functional groups decreased with the increases of carbonization temperature. Thus, the best carbonization temperature was 400 ℃. The adsorption capacity of ICs with different iron salts content for As (Ⅲ) and As (Ⅴ) were performed and we found the composite with 3% iron salts ratio have best absorption performance. Scanning electron microscopy and EDS spectrum revealed that carbon fibers remain intact fiber morphology after annealing at 400 ℃, and the surface of composite materials were adhered a layer of iron particles. The adsorption performance for As(Ⅲ) and As(Ⅴ), ICs have excellent stability in the range of pH 4.0 to 7.0, the maximum amount adsorption for As (Ⅲ) and As (V) were 29.1 mg g-1 and 25.6 mg g-1, respectively. The ICs overcome the difficulty of recovered problems of nanoscale zero valent iron particles.2. Three-dimensional honeycomb-liked porous-structured nZVIs/chitosan composite foams (ICCFs) were fabricated via a freeze-drying process. By investigation of the mechanical property and adsorption capacity, we found the optimal freezing temperature was of -80℃ and the optimal ratio of nZVIs/chitosan was 2:5. The ICCFs is formed by the accumulation of equal thickness chitosan films with the same spacing, and uniform microporous were observed on the surface of ICCFs. The isothermal adsorption revealed the maximum saturated adsorption amount for As(Ⅲ) and As(Ⅴ) ions by the ICCFs was 114.9 mg g-1 and 86.87 mg g-1, respectively, which were higher than the other reported nZVIs/chitosan composites. The adsorption kinetic experiments indicated that the rates of As(Ⅲ) and As(Ⅴ) adsorption were fast and equilibrium were achieved in about 120 min in the whole adsorption process. The study on the pH influence of arsenic solution on the adsorption of As(Ⅲ) and As(Ⅴ) ions by the ICCFs showed that the equilibrium adsorption amount is almost unchanged with pH value in the range of 4.0 to 7.0. In addition, ICCFs presented strcture-enhanced remove for As(Ⅲ) and As(Ⅴ) compared with other nZVIs/chitosan composites. Porous-structured nZVIs/chitosan composites not only in favour of nZVIs contacting with arsenic, but also iron ions released from nZVIs can be complexed by chitosan in ICCFs avoiding the secondary pollution.