Untitled

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 *Corresponding author. Presented at the 9th Environmental Science and Technology Symposium, September 1–3, 2005, Rhodes, Greece. Organized by the Global NEST organization and prepared with the editorial help of the University of Aegean, Mytilene, Greece and the University of Salerno, Fisciano (SA), Italy. 0011-9164/07/$– See front matter © 2007 Elsevier B.V. All rights reserved

The results presented in this study suggest that precipitation at room temperature can be used as a treatment process for the recovery of constituents existing in aqueous solutions obtained from hydrometallurgical procedures. The benefits of using dilute acidic solutions for the selective removal of constituents are reflected at the following stages, when the recovery of constituents using precipitation processes occurs. Ionic strength is limited, making the quantitative precipitation easier. The temperature increase is negligible (2– 3°C in this study) and the entire procedure becomes simpler. In the presence of halogens and toxic metals, such as lead in this study, the main product (precipitate) of the process would be the hydroxy salt of the metal, making feasible the effective recycling of specific waste types. Lead bromide hydroxide would be the major solid phase when synthetic aqueous inorganic solutions that contain lead and bromide in the appropriate stoichiometries are mixed in the pH area 4–7, whereas its formation might initiate at even lower pH values. The hydrated lead bromide hydroxide (Pb(OH)Br·H2O) solubility in the de-ionized water would be approximately 5 mg/100 ml H2O, whereas its solubility in 0.1 M HNO3 was found approximately 22.83 g/L, a value that should be taken into consideration when solid wastes containing similar solid phases are found. All the results and the respective literature research suggest that the nature of the hydroxy metal bond as well as all the relative characterization data should be supported and examined in a more detailed manner, in relation with the respective theoretical background.