| Arsenic is a toxic element, it can cause canceration of skin, liver, kidneys and many other organs when its concentration exceed sanitary standards of drinking water (10?g/L). It is getting more and more attention because of the frequently breaking out of endemic arsenic pollution incidents in recent years. Therefore, it is necessary to develop an economical and viable arsenic removel technology.In this research, three commercial activated carbon (AC) N1, N2, N3 were used to remove As(?)(trivalent arsenic) and As(?) (pentavalent arsenic) from aqueous solution,respectively. The adsorption behaviors of arsenic on the three ACs were followed the pseudo-second-order kinetic model. The initial adsorption rate of N1 was much faster as for the 0.405 mg/(g·h). The adsorption of As(?) and As( V) on the surfaces of N1 and N2 fitted to the Langmuir model, but the adsorption on N3 fitted to the Freudlich model. The adsorption capacity of As(?) on N1 was 3.69mg/g which was obviously higher than on N2(1.97mg/g) and N3 (0.54 mg/g); and the adsorption capacity of As(V) on N1 was 2.88mg/g which was also signifigantly higher than N2 (1.50mg/g) and N3 (0.58 mg/g). Therfore, N1 showed certain advantages from the initial rate and the adsorption capacities.The adsorption of As (?) on N1 was a spontaneous exothermic process and mainly physical adsorption, which was accompanied by chemisorption. The change of the solution pH value may change the form of As (?) and the charge of ACs surface. With the increase of pH, the adsorption capacity of As (?) on N1 firstly increased and then decreased, and the optuim pH was 6 (adsorption capacity was 4.048mg/g). Further studies showed that the introduction of Na+ and Cl- might compete active sites with As (?), which led to the adsorption capacity of As (?) decreased with the increase of ionic strength. In addition,the coexisting Fe2+ also affected the adaorption of As (?). The adsorption of Fe2+ on N1 could provide more active sites for As (?),which firstly increased the adsorption capacity of As (?)and then tended towards stability with the increase of the Fe2+ concentration.The adsorption of As (?) on N1 was also a spontaneous exothermic process and mainly physical adsorption, which was accompanied by chemisorption. With the increase of pH, the adsorption capacity of As (?) on N1 decreased after increase, and the optuim pH was 7(adsorption capacity was2.931mg/g). In addition,the adsorption capacity of As (?) on N1 firstly increased and then decreased with the increase of ionic strength. Electronic shielding effect was the main reason for the increasing adsorption capacity in the smaller ionic strength,but the competitive adsorption between Na+, Cl- and As (?) played a major role in the larger ionic strength. When the concentration of Fe2+ increased,the adsorption capacity of As (?)on N1 increased gradually. The substantial increase in adsorption capacity was mainly due to the strong binding ability between the iron on AC surface and As (V).Basing on the characterization results of surface properities of ACs and effects of different factors on the arsenic adsorption, the electrostatic interaction and physical adsorption could play the major role for the adsorption of arsenic on the ACs surface. However, the chemisorption was the possible reason for multiple increase of the adsorption capacity of As(?) with the addition of Fe2+.The research of column breakthrough curve indicated that the adsorption capacities of As(?) and As(?) gradually decreased with the increase of column height. When the column height increased from 5cm to 20cm, the adsorption capacities of As(?) decreased from 8.153mg/g to 4.076 mg/g and the breakthrough time extended from 6 days to 12 days.Meanwhile, the adsorption capacities of As(?) decreased from 5.435mg/g to 2.718 mg/g and the breakthrough time extended from 4 days to 8 days. But the static adsorption abilities were greatly improved. |
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