Correlation between the limiting pH of metal ion solubility and total metal concentration

As an alternative to species distribution diagrams (pM vs pH curves in aque ous solution) drawn for a fixed total metal concentration, this work has de veloped simple linear models for correlating the limiting pH of metal ion s olubility-in equilibrium with the least soluble amorphous metal hydroxide s olid phase-to the total metal concentration. Thus adsorptive metal removal processes in complex systems can be better designed once the limiting pH of heavy metal solubility (i.e., pH*) in such a complex environment can be en visaged by simple linear equations. pH* vs pM, (M-t = total metal concentra tion that can exist in aqueous solution in equilibrium with M(OH)(2(s))) li near curves for uranyl-hydroxide, uranyl- carbonate-hydroxide, and mercuric -chloride-hydroxide simple and mixed-ligand systems and cupric-carbonate-hy droxide complexes in equilibrium with mixed hydroxide solid phases may enab le the experimental chemist to distinguish true adsorption (e.g., onto hydr ous oxide sorbents) from bulk precipitation removal of the metal and to int erpret some anomalous metal fixation data-usually attributed to pure adsorp tion in the literature-with precipitation if the pM(t) at the studied pH is lower than that tolerated by pH* vs pM(t) curves. This easily predictable pH* corresponding to a given pM(t) may aid the design of desorptive mobiliz ation experiments for certain metals as well as their adsorptive removal wi th the purpose of simulating metal adsorption and desorption cycles in real complex environments with changing ground water pH. (C) 1999 Academic Pres s.