Removal of Arsenic and Chromium Oxyanions by Hydrous Tin Dioxide and Tin(IV)-Loaded Exchangers

The potential of tin-loaded poly(hydroxamic acid) ion exchange resin (SnPHA), hydrous tin dioxide (SnO2.xH2O) and hydrous tin dioxide-loaded poly(hydroxamic acid) resin (SnOPHA) to remove heavy metals As(V), As(III) and Cr(VI) from aqueous solution was investigated. Poly(hydroxamic acid) resin was prepared from poly methyl acrylate-divinyl benzene copolymer (PMA). The ester group of the PMA was converted to the hydroxamic acid using the hydroxylamine in an alkaline solution. The SnPHA was prepared by shaking the PHA resin with SnCl4 solution. SnO2.xH2O was prepared by neutralizing a Sn(IV) chloride solution with ammonia solution. The XRD result proved that the SnO2.xH2O prepared is pure. The SnOPHA was produced by direct treating SnPHA with ammonia solution. The XRD result also contributed clear information about the oxidation stated of Sn(IV) in the PHA resin. In order to understand the sorption characteristics of As(V), As(III) and Cr(VI) by the sorbents, batch and column studied were performed under various experimental conditions. The parameters studied were pH, temperature, contact time, isotherm study, sorbent dosage, presence of competitive anions, flow rate and sorption-desorption cycles. The sorbents were also tested to remove arsenic and chromium from industrial waste water samples. The results of batch study indicated that the sorption process by the sorbents was pH dependent and endothermic. It was found that the SnO2.xH2O sorbent has the highest sorption capacity for As(V), As(III) and Cr(VI), followed by SnPHA and SnOPHA. Kinetic study showed that uptake of As(V) ion by the sorbents reached equilibrium after about 13 hours and about 10 hours for Cr(VI) sorption. The maximum sorption capacity of the SnPHA for As(V) and Cr(VI) at room temperature determined from the Langmuir isotherm were 38.50 mg-As/g-resin and 22.12 mg-Cr/g-resin, respectively. Meanwhile, the maximum sorption capacity of the SnOPHA were 8.30 mg-As/g-resin and 14.93 mg-Cr/g-resin and the maximum sorption capacity of the SnO2.xH2O were 64.10 mg-As/g-sorbent and 28.57 mg-Cr/g-sorbent. The uptake increased with increasing sorbent dosage. In the presence of phosphate, sulphate and chromium anions, As(V) uptake decreased. In desorption study, As(V) and Cr(VI) could be removed almost quantitatively from SnPHA and SnOPHA by eluting with a 0.2M NaOH solution. However, a rather low flow rates have to be applied for sorption using the column method. The SnPHA column could be used at least for 3 cycles and 2 cycles for SnOPHA for removal of As(V) ions. More than 86 % of arsenic and chromium were successfully removed from industrial waste water samples by SnPHA.

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