Raman and Fourier transform infrared spectroscopic study of pyromorphite-vanadinite solid solutions

Due to the great range of the application fields for apatites, there is a strong need to complete the data set determining the properties of these minerals. In this study, Raman and Infrared spectra of the phases from pyromorphite Pb₅(PO₄)₃Cl - vanadinite Pb₅(VO₄)₃Cl series were investigated. Totally, 9 samples (2 end-members and 7 solid solutions of the series) were synthesized at 25°C and pH=3.5, and analyzed. In the Raman and Infrared spectra of the studied Pb-apatites, the bands typical for the vibrations in the PO₄ and the VO₄ tetrahedra appeared. The bands attributed to the stretching vibrations (ν₁, ν₃) occurred in the 1050-910cm^-1 and 830-720cm^-1 regions, whereas the bending vibrations (ν₂, ν₄) were visible at the 580-540cm^-1, 430-380cm^-1 and 370-290cm^-1 range. The position of the bands depended on the P/(P+V) ratio in the analyzed solid, since there are differences in the ionic radii and the atomic mass of P⁵⁺ and V⁵⁺, which affect the bong lengths, bond forces and the banding energies of the substituting tetrahedra. The analysis allowed observing gradual shifts of the bands caused by the replacement of phosphorous with vanadium in the studied phases. The positions and the intensities of selected bands are proposed to serve as a semi-quantitative estimation of the chemical composition of the phases from the pyromorphite - vanadinite series.

Removal of lead and phosphate ions from aqueous solutions by organo-smectite

Smectite has been modified using hexadecyltrimethyl ammonium bromide in an amount of double cationic exchange capacity. This alteration makes it possible to use organo-smectite as a sorbent to remove anionic forms. The experiment consisted of the interchangeable sorption of phosphate(V) and lead(II) by organo-smectite. Research was carried out with varying pH (2-5) and various concentrations (0.1-5 mmol/L). Organo-smectite with previously adsorbed lead ions removed more phosphate than the untreated organo-smectite. Experimental data show that lead is more likely to absorb on the organo-smectite than on the organo-smectite with previously adsorbed phosphate ions. It follows that the most effective use of the organo-smectite is through the sorption of first - Pb cations and then PO4 anions. With an increasing concentration of Pb(II) or P(V), the sorption efficiency increases. The maximum sorption efficiency of lead and phosphate ions is observed at pH 5. This enables the removal of harmful lead and phosphorus compounds from waste water and immobilizes them on the sorbent's surface. The alternating reactions of lead and phosphorus ions result in the crystallization of brompyromorphite Pb5(PO4)3Br.