Recitation Assignment 5

Due at the end of class

 Recitation Problems:

1)      Input the following modified water from homework problem (1) into PhreeqC, using the PhreeqC database.

TITLE  GWTP

# Thomas C. Green Water Treatment Plant  (GWTP)utilizes Town Lake and provides tap water for       # downtown Austin                           

SOLUTION 1

        units   ppm

        pH      9.9

        temp    25

        Ca      17

        C(+4)   10 as HCO3-

        end

            What is the SI w.r.t calcite? Is it under-saturated or oversaturated?

2) Use PhreeqC for WIndows with the Lawrence Livermore National Labs database (LLNL) database to calculate the equilibrium speciation and SI's of the following geyser water from El Tatio.

TITLE Tatio water species

SOLUTION 1 #TAT03-011 Horseshoe Geyser water

            units   ppm

            pH      6.67

            temp    81.5

        Cl              6924

        Br              8.39

        S(6)            76.9 as SO4-2

        Li              39.12

        B               174.66

        Na              3729

        Si              155.67

        K               561.2

        Ca              266.5

        Cs              17.4

        As(3)           24.7

        As(5)           18.83

        Al              0.216

        P               1.663

        Ni              0.0498

        Cu              0.0718

        Rb              6.991

        Sr              4.758

 END

(a)   What does the model predict the concentrations of the various As(V)

species to be in mMol? What about in ppm-As(V)?

Take a look at the following Bjerrum plot from another spring at 60 C.  The pH of this spring is about 6.3.

(b)  Print or copy this graph, label the axes, and plot the pKa of H₂AsO₄^- and pH of the water as dashed vertical lines (by hand) Then estimate the molar concentrations of the various As(V) species in this water.

3)  Discharge water from an ion exchange process contains 0.25 moles of NaOH per liter. It must be partially neutralized by the addition of H₂SO₄ prior to discharge. The required final pH is 10. What volume of a 1 M H₂SO₄ solution must be added per liter of waste? The temperature is 25 deg. C and the ionic strength is approximately 0.1.