Metals in Aqueous Systems Questions

PRINCIPLES OF WATER CHEMISTRY

METALS IN AQUEOUS SYSTEMS

HOMEWORK-08

PLEASE NOTE THE UNUSUAL DUE DATE FOR THIS HOMEWORK

DUE ON MONDAY 11/30/2020, at 5:00 PM

  • Should be typed since using MINTEQ
  • If typing, using “Word”, select “INSERT” and “ EQUATION” and then “ INSERT NEW EQUATION” to type in chemical and mathematical formulas.
  • SUBMISSION should be THROUGH CANVAS ONLY. Email submissions are not be accepted

Question (100 points) – Using MINTEQ and following the solution strategy given in Lecture-35, solve the following problem by describing in details the different steps used to address the 4 points below.

A water with a pH of 8.1 contains 2.0 meq/L of alkalinity, 0.2 mmol/L of TOTPO4, and a negligible concentration of Ca2+. In this water, the alkalinity (ALK) is all from PO4 and CO3 species. If lime (Ca(OH)2) is added to this aqueous solution with the goal of removing 95% of TOTPO4 by precipitation of Ca5OH(PO4)3(s):

  1. Draw a log C – pH diagram showing Ca2+ activity in equilibrium with each of two solids: CaCO3(s) and Ca5OH(PO4)3(s), for the initial TOTCO3 and TOTPO4. Which solid will precipitate first?
  2. Plot pH vs. lime dose, if no solid precipitates. Consider additions of 0 to 5×10-4M lime. Add a curve to the plot from part (a) showing log(Ca2+) vs. pH during the titration.
  3. Repeat part (b), allowing for precipitation of solids. How much lime must be added, and what will the pH be, when the TOTPO4 target is reached?
  4. If more lime is added, can the second solid precipitate? If so, under what conditions? If no, why not?
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