ENCE 433 Dr. Alba Torrents

ENVIRONMENTAL ENGINEERING ANALYSIS Fall 1996

Homework Set #7 Out: November 7 Due: November 12

SOLUBILITY

  1. An acid rain falls onto a watershed for which the natural buffering capacity of the soil has already been depleted. Acidification of lake waters by acid deposition is believed to cause release of metal ions from sediments. We can approximate the solubility of metal ions with the solubility of the hydroxide:


A) Plot the metal ion concentrations as a function of pH (for the three metals)

B) Examine the effects of decreasing pH on the concentration of aluminum in lake water, assuming that it is in equilibrium with the sediments. Consider a-Al(OH)3 (s) to be the sedimentary phase of aluminum. Consider the following reactions involving aluminum:

  1. Construct a solubility diagram showing all of the dissolved species of aluminum listed above and showing AlT = total dissolved aluminum as a function of pH.

(b) Evaluate and compare AlT and [Al3+] at pH 6.5 and at pH 4.5.