Removal and recovery of cobalt from Co(II)–containing water samples by dithiocarboxyl polyethyleneimine

Abstract

A water-soluble macromolecule flocculant was developed for the removal and recovery of Co(II) from water samples. The flocculant, called dithiocarboxyl polyethyleneimine (DTPEI), has the functions of chelation, precipitation, and flocculation for Co(II). The effects of settling time, hydraulic conditions, initial Co(II) concentration, pH value, coexisting common compounds, and turbidity on the removal of Co(II) by DTPEI were investigated through flocculation tests. DTPEI could effectively remove Co(II) for different initial concentrations of Co(II) in water samples, and the settling velocity of the flocs formed between DTPEI and Co(II) was very rapid. Because pH value may affect the Co(II) species, the protonation of the functional groups on DTPEI molecular chains, and the surface charge of the flocs, the removal rate of Co(II) would increase by raising pH from 2.0 to 7.8. The maximum removal rate of Co(II) reached 100% at pH 3.0–7.8. The presence of common compounds (KCl, NaCl, CaCl2, MgCl2, NaNO3, and Na2SO4) in water samples had less impact on the Co(II) removal. Furthermore, when the turbidity coexisted in the water samples containing Co(II), Co(II) and turbidity were simultaneously removed by DTPEI because of the adsorption bridging effect and the sweep function. The maximum removal rate of turbidity could reach 99.8%. However, the existence of turbidity inhibited the Co(II) removal due to the consumption of DTPEI for turbidity. Cobalt could be recovered from the flocs of DTPEI–Co by using acid solutions because DTPEI–Co may be decomposed in high-concentration acid solutions. The recovery of cobalt was 77.1% in 2.0 mol/L of HNO3 solution for soaking 72 h. The results of FTIR spectra indicate that the chelating reaction occurred between Co(II) and C(S)SH and NH2 on DTPEI molecular chains to form the DTPEI–Co flocs.