Published:January 01, 1994
Although water may contain excess inorganic compounds of many kinds, heavy metals are one of the more common problems. Remediation (removal) of the compounds is commonly done by pH control. That is, the pH is raised to a level at which the metal is insoluble. Then, the precipitated metal is made to flocculate so that it will settle out of the water column. After the metal settles, the water can then be brought back to a normal pH by adding an acid.
Details of the above processes are beyond the scope of this course and text. A review of the above process, plus other processes for removing metals (ion exchange, reverse osmosis, electrodialysis, and distillation) are given in Nyer (1985). The thermodynamic equilibrium basis for the solubility of metals (and nonmetals) as a function of pH and Eh is reviewed in Fetter (1993). A more complete description is given in Garrels and Christ (1965).
Figures 10.1 and 10.2 (adapted from Garrels and Christ, 1965, Figs. 7.5d and 7.5e) are examples of how the stability field of an inorganic species, iron in this case, can be described using Eh-pH plots. Figure 10.1 shows that the maximum amount (activity) of dissolved Fe+2 that can exist in solution decreases both with increasing Eh and increasing pH. Figure 10.2 shows that the activity of dissolved Fe+3 that can exist in solution is unaffected by Eh (in the hematite + water field) but decreases with increasing pH.Comparison of the two figures shows that Fe+3
Figures & Tables
Introduction to Environmental Hydrogeology
These notes have been written to supply supporting material for a “short course” introduction to environmental hydrogeology. The assumption is that most people who take the short course (or purchase the notes without taking the short course) will be geologists, although the information could be useful to engineers or other scientists who desire an introduction to environmental consulting in general, or hydrogeology in particular. The notes, and course, are an introduction – a partial survey - of some aspects of environmental geology, with particular reference to subsurface hydrogeology and remediation of sites contaminated with petroleum hydrocarbons. No claim of completeness is made. Regulatory programs vary from state to state. The regulatory framework used in the state of New York is sometimes given as an example. The reader should be aware that rules and procedures may differ in other states.