REMOVAL OF ARSENIC CONTAMINATED IN WATER BY CHITOSAN-MODIFIED NANOSCALE ZERO-VALENT IRON (CNZVI)

Abstract

Chitosan-modified nanoscale zero-valent iron (CNZVI) was synthesized for arsenic removal from water. Acetic acid was suitable as a solvent to dissolve chitosan facilitate the CNZVI synthesis. Surface morphology, the particle size, and the point of zero charge of NZVI and CNZVI were characterized by SEM/EDS, TEM, and salt addition method, respectively. The surface images showed the more dispersion of iron particle in CNZVI than in bare NZVI and also the coverage of chitosan over iron particles were found. Chitosan can reduce the agglomeration of NZVI particles. The particle size of CNZVI was smaller than NZVI. The point of zero charge of NZVI was at pH 7.8, while that of CNZVI is in the range of 7.83-10.1. Batch experiments were carried out to examine the influence of weight percent of chitosan loading (2.5-30%wt) in the CNZVI, and the initial solution pH including acidic, neutral, and basic (4, 7, 9) conditions. Both arsenite and arsenate removal rate increased with higher weight percent of chitosan loading but decreased with higher initial pH. In addition, the efficiencies of CNZVI for arsenic removal did not change significantly for the three investigated pH conditions, when higher percentage of chitosan loading was applied. The isotherm and kinetic adsorption experimental data fit well into Langmuir isotherm and the pseudo second-order model. The mechanisms of arsenic removal by CNZVI are proposed. Three kinds of mechanism pathways consist of adsorption of chitosan and As species, adsorption of iron corrosion products and As species, and co-precipitation of As(V) and iron corrosion products. Chitosan could retard the oxidation reaction of NZVI. CNZVI, therefore, could retain its activity on arsenic removal higher than NZVI, in the shelf-life study between 2-30 days.