The preparation and properties of iron-walnut shell powder microelectrolytic spherical fillers

In order to solve the issues of caking, loss, and effluent color reversion in the application of traditional microelectrolysis, the iron-walnut shell powder microelectrolytic spherical filler was developed in this paper. The filler was prepared by walnut shell powder, iron powder, sodium silicate, and sodium humate activated by ZnCl₂ as raw materials and calcined at high temperature. The effects of the mass ratios of Fe to walnut shell powder, sodium silicate content, sodium humate content, calcination temperature, and time on the removal rate of methylene blue by the spherical fillers were investigated, so as to determine the optimal preparation conditions of the spherical fillers. The pore-forming structure and the composition of the spherical fillers were also analyzed by an X-ray diffractometer (XRD), a scanning electron microscope (SEM), and an energy spectrometer (EDS). The results show that the optimal preparation conditions for the spherical fillers of 5 mm are as follows: the mass ratio of iron powder to walnut shell powder treated by 15% ZnCl₂ is 1:1, sodium silicate is 15%, sodium humate is 20%, the calcination temperature is 800 °C, and the calcination time is 3 h. Compared with the conventional microelectrolysis, the removal rate of methylene blue by the spherical fillers can finally reach the same level as it did, and the phenomena of the filler hardening and clogging can be avoided.