WANG Hui-min, et al/Trans. Nonferrous Met. Soc. China 21(2011) 2542 2547 2545
NH4+ makes great contribution to jarosite precipitation and its concentration has a large influence on the amount of precipitation. Ammonium sulfate [(NH4)2SO4] concentration can be set at 0.5 and 3.0 g/L respectively in medium with pH=1.5 while other ingredients remain constant. The amounts of precipitation that change over time are acquired. The result is shown in Fig. 5.
Fig. 6 FTIR spectrum of BPFS
Fig. 5 Effect of (NH4) 2SO4 concentration on precipitation
As the concentration of (NH4)2SO4 decreases from 3.0 to 0.5 g/L, the amount of precipitation is significantly reduced while the oxidation rate of Fe2+ is not changed. In addition, considering reagent usages and production costs, (NH4)2SO4 concentration of 0.5 g/L is more favorable for the preparation of BPFS.
3.2 Characterization of prepared BPFS
The BPFS prepared under the optimum condition is characterized. pH of the BPFS ranges from 1.5 to 2.2, which is higher than that of the PFS prepared by conventional methods and can reduce corrosion for the reactor. The total iron content of the BPFS is 43.87 45.24 g/L and the basicity is 17.5% 22.7% which is higher than that of the most PFS previously reported, resulting in better flocculability.
Moreover, it is suggested that the BPFS coagulants consist of species containing both Fe and —OH by the analysis of FT-IR spectroscopy (Fig. 6). In particular, peak at 821 cm 1 corresponds to Fe—OH—Fe symmetrical stretching vibrations, peaks at 1 020 and 639 cm 1 are associated with a Fe—O—H bond, peaks at 3 460 and 1 640 cm 1 are related to H—O—H stretching vibrations and peak at around 1 100 cm 1 is the characteristic absorption peak of SO42 [19 23].
3.3 Application of BPFS
The removal efficiencies of COD, decolorization and Zn2+ by the BPFS were investigated at different pH, the results are shown in Fig. 7.
Generally, the treatment effect of the PFS on contaminated water varies with pH. As the BPFS is
Fig. 7 Removal efficiencies of COD (a), decolorization (b) and Zn2+ (c) by BPFS at different pH