Precipitation of Lead Species in a Pb - H2O System

Abstract

Precipitation of metallic species in either, liquid-liquid, solid-solid, or liquid-solid systems is a current phenomenon related with the formation and/or deposition of second phases. An example of the above is the deposition of some precipitated species on ore particles during milling, changing their surface properties and affecting the process of capture during flotation. Precipitation of species also occurs during the waste water treatment. Despite the fact that several procedures have been designed to clean water contaminated with heavy metals (i.e., activated zeolite and membranes, gas dispersion devices, bird feathers, biological procedures, etc.) the mechanisms describing the formation of such phases or species are not well understood. This work establishes from a thermodynamic point of view the conditions (pH, electrochemical potential, ionic strength, activity coefficient) to predict the formation of certain species (precipitated or dissolved) in distilled water contaminated with lead by adding Pb(NO3) 2, and open to the atmosphere. The pH of the media was varied from 3 to 13. The proposed mechanism of reaction for the system tested here is: Pb(NO 3)2 + H 2O→Pb 2+ + PbSO 4 → Pb 3(CO 3)2 (OH) 2. Being the formation of lead carbonate explained by considering the replacement of sulfates or sulfites, to carbonates in a system reacting with the atmospheric air. From the information derived in this work, it is possible to design a process for cleaning water contaminated with heavy metals through the route sedimentation – flotation, and to predict or avoid the formation of certain species on ore particles that reduce the metallurgical efficiency of the flotation process.