Lead and bromide precipitation from aqueous acidic solutions. Potential exploitation in industrial applications

Abstract

Precipitation of lead and bromide, followed by careful crystallization, is usually discussed when the productionor synthesis of lead bromide is involved. However, there are numerous issues, especially concerning the precipitationof lead bromide hydroxide (Pb(OH)Br) and its derivatives in the neutral pH range (6.5–8), that has not beendiscussed in detail. The importance of the additional research needed for this issue can be justified by the fact thatsimilar pH values can be observed in natural waters. The obtained data suggest that lead bromide hydroxide wouldbe the major solid phase of the resulting precipitate when lead and bromide exist in an aqueous solution in a properstoichiometry and in the pH range 4.5–8 irrelevantly from the background solution (i.e. acetates or nitrates) or themethodology of precipitation (i.e. mixture of the respective synthetic salts or titration of a concentrated industrialacidic solution containing lead and bromide). The latter was additionally supported by the fact that lead bromidehydroxide was recorded as the end product of a titration which included also ions other than lead and bromidesuggesting that, even in the presence of inhibitors in low concentrations, lead bromide hydroxide would bequantitatively precipitated. Additionally, in terms of application, direct precipitation can be certainly examined asa potential treatment option for small scale hydrometallurgical procedures, although the appropriate purificationstage 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 hazardoussolid 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 thechemical 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 solubilityissues of the synthetic Pb(OH)Br are presented.