Adsorption Of Trace Levels Of Bromate From Drinking Water By Nano Crystalline Akaganeite(β-FeOOH)-coated Quartz Sand (CACQS)

Bromate does not occur in natural waters, but it is formed during ozonation which is commonly used in water treatment because of the presence of bromide. Bromate has been classified by the International Ageney for Researeh on Cancer (IARC) as a possible human carcinogen, and in China, maximum contaminant level (MCL) of bromate is10μg/L in drinking water sanitary standard (GB5749-2006) and drinking natural mineral water (GB8537-2008), thereby the research of control and removal of bromate is urgent. As the present technologies for bromate control or removal have some deficiencies, the use of adsorption is becoming research hot spot inrecent years due to its low cost and convenient.This study synthesised the adsorption material nano crystalline akaganeite (β-FeOOH)-coated quartz sand (CACQS). Batch experiments were carried out as a function of various operational conditions such as adsorbent dosage (20-160g/L), initial pH (3-12), contact time (1-240min), initial bromate concentration (0.6-10mg/L), temperature (288K,298K and308K) and competition anions (F-、NO3-、 OH-、SO42-、PO43-、CO32-�'�Cl-). The thermodynamics and kinetics of adsorptive process were also investigated. The main conclusions are as follows:1. The adsorption occurred quickly and the time required to achieve equilibrium is20min. pH has a great influence on bromate removal, the maximum adsorption of bromate is about1.5g/g in the pH range from3.0to10.0and decreases sharply at pHs over10.0. The optimum bromate removal was observed over a wide pH range of3-10, suggesting that the CACQS can be successfully utilized in drinking water processes. Lower adsorption efficiency for bromate was observed with the increasing of temperature. The adsorptive capacities of bromate under three different test temperatures (288K,298K,308K) were47.39μg/g,45.75μg/g�'�29.07μg/g, respectively.2. Coexistence anions in water can have an influence on bromate removal with CACQS. The degree of anions suppression on bromate was PO43->SO42->CO32-NO3-F-�'�OH-ion-exchanged with Cl-occurs to a certain extent during the BrO3- adsorption process, and have a higher suppression compared with CO32-3. The greater correlation coefficients (>0.99) at all the temperatures indicated the Langmuir model fit the data better than the Freundlich model in the present study. The pseudo-second-order model describes the experimental data well. The negative ΔG°values indicate that the adsorption process is spontaneous and feasible. The value of ΔH°for bromate adsorption is-6.57kJ/mol, which is negative and lower than40kJ/mol, suggesting that interaction between bromate and CACQS is exothermic and that the adsorption can be described as a physical process.