Lead and bromide precipitation from aqueous acidic solutions. Potential exploitation in industrial applications
Precipitation of lead and bromide, followed by careful crystallization, is usually discussed when the production or synthesis of lead bromide is involved. However, there are numerous issues, especially concerning the precipitation of lead bromide hydroxide (Pb(OH)Br) and its derivatives in the neutral pH range (6.5–8), that has not been discussed in detail. The importance of the additional research needed for this issue can be justified by the fact that similar pH values can be observed in natural waters. The obtained data suggest that lead bromide hydroxide would be the major solid phase of the resulting precipitate when lead and bromide exist in an aqueous solution in a proper stoichiometry and in the pH range 4.5–8 irrelevantly from the background solution (i.e. acetates or nitrates) or the methodology of precipitation (i.e. mixture of the respective synthetic salts or titration of a concentrated industrial acidic solution containing lead and bromide). The latter was additionally supported by the fact that lead bromide hydroxide was recorded as the end product of a titration which included also ions other than lead and bromide suggesting that, even in the presence of inhibitors in low concentrations, lead bromide hydroxide would be quantitatively precipitated. Additionally, in terms of application, direct precipitation can be certainly examined as a potential treatment option for small scale hydrometallurgical procedures, although the appropriate purification stage cannot be avoided. The obtained results also verified that when the methodology of limited acid demand would be initially applied for the selective leaching of constituents (lead and bromide here) from industrial hazardous solid wastes, then the precipitation of the resulting aqueous solution (leachate) would be possible and feasible. Furthermore, dissolution experiments of synthetic lead bromide hydroxide proved that although the nature of the chemical bonds limits its dissolution in water, its solubility is high enough to be characterized as a toxic pollutant, whereas in acidic environments all the respective compounds of the Pb(OH)X where X the respective halogen, would be highly soluble. Also, certain other characterization data, such as SEM, FT-IR and XRD as well as solubility issues of the synthetic Pb(OH)Br are presented.
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