生物法制备聚合硫酸铁及其应用研究_英文_(3)

2544 WANG Hui-min, et al/Trans. Nonferrous Met. Soc. China 21(2011) 2542 2547

Figure 2 shows the conversion of Fe2+ versus time at pH value of 2.0, 1.8 and 1.5. The conversion of Fe2+ is stronger at pH 2.0 than that at pH 1.8 and pH=1.5 in the initial stages; however, it is not different at the end of the experiment (after 100 h) with conversion of about 90% at pH=2.0, 1.8 and 1.5. It is found that the precipitation of jarosite [MFe3(SO)(OH)6] can be easily generated at initial pH value of about 2.0, especially with high iron concentration, resulting in inhibition occurring in the oxidation of Fe2+. Therefore, initial pH value of 1.5 is considered to be appropriate for the preparation of BPFS.

impact on the conversion of Fe2+. Thus, 10% inoculum for the preparation of BPFS is chosen. 3.1.4 Effect of initial iron concentration

The effect of the initial Fe2+ concentration on the BPFS preparation was studied by changing the Fe2+ concentration from 35 to 45 g/L. As shown in Fig. 4, with the increase of Fe2+ concentration, the average oxidation rate of Fe2+ decreases, and the color of BPFS gets darker because the growth of bacteria requires proper amount of Fe2+. Low Fe2+ concentration cannot provide sufficient energy to the growth of bacteria and causes the prepared BPFS to be low in iron content and less useful in application. However, too much Fe2+ can inhibit the growth of bacteria. Based on the comparison of the growth of bacteria under different Fe2+ concentration conditions, it is concluded that with the initial Fe2+ concentration of 40 g/L, Fe2+ oxidation rate is more stable and BPFS with good performance can be obtained.

Fig. 2 Impact of initial pH on conversion of Fe

2+

3.1.3 Effect of inoculation amount

To investigate the effect of inoculation amount on the BPFS preparation, experiments were conducted with 5%, 10%, 15% and 20% inoculum. The results are shown in Fig. 3.

Fig. 4 Impact of different initial Fe concentration on conversion of Fe2+

2+

Fig. 3 Impact of inoculum on conversion of Fe2+

Clearly, the conversion of Fe2+ is much lower with 5% inoculum, and the conversion of Fe2+ is only 55% after 56 h. However, with the addition of 10% to 20% inoculum, the conversions of Fe2+ are not significantly different and the conversion of about 98% is obtained after 56 h. It is illustrated that with 10% or more inoculum, the amount of inoculum does not have much

3.1.5 Effect of reaction solution composition on

preparation of BPFS

A certain amount of precipitation can be generated during the preparation of BPFS by microbes. Based on the analysis of X-ray diffraction (XRD), the precipitation is identified as pyrite vanadium with formula MFe3(SO4)(OH). However, the precipitate produced during the preparation of BPFS is undesirable because it can cause the scale in bioreactor and affect the transmit between substrate and metabolites, resulting in deficiencies of the nutrients such as O2, CO2 and substrate Fe2+ and a decrease in the reaction rate. Thus, it is very important to obtain a suitable culture medium with good oxidative activity of bacteria as well as less precipitation [15 18].

As the chemical formula for jarosite precipitation is MFe3(SO4)(OH), where M may be K+, Na+, NH4+ or H3O+, so the precipitation generation is related to the medium pH, cation species and concentration. Usually,