# Practical 5- Assessed Summary Practical. Acid waste with heavy metal contaminants: Treatment.

Practical 5- Assessed Summary Practical. Acid waste with heavy metal contaminants: Treatment.

This practical will integrate various aspects of what we have done so far in the course.

There are 4 questions, each worth 25 marks.

There is an industrial plant which produces a waste stream effluent of extremely acidic fluid. Before treatment, this is essentially a pH = 1 solution of HCl. The company uses a mixture of crushed minerals to treat the waste and neutralize the acid. They use a mixture of crushed olivine and calcite, but unfortunately the bulk process of preparing the silicate rock is not able to remove all of the impurities so there is also an iron oxide mixed into the treatment. The mineral mass percentages are: 40% forsterite (Mg-olivine), 50% calcite, 10% magnetite. Rate laws for the dissolution of all three of these minerals have been measured.

Surface Area: 500 cm2/g estimated to be equal for all three minerals.

Rate laws

Olivine

Rate = 1 e-13 moles cm-2 s-1

Calcite

Rate = 1 e -11 moles cm-2 s-1

Magnetite

Rate = 1 e -12 moles cm-2 s-1

Gas equilibria

Fluid is in equilibrium with atmospheric oxygen (fugacity = 0.2 atm) and atmospheric CO2 (fugacity = 10^-3.5)

Fluid starting composition

Ca++         1 mmol/kg

Mg++       1e-12 mmol/kg

SiO2(aq)  1e-12 mmol/kg

Fe++        1e-12 mmol/kg

Cl-             100 mmol/kg

Na+          100 mmol/kg

Carbonate, aqueous oxygen, and H+ must also be part of the basis, with amounts given by the parameters listed in other sections above.

1) What mass of treatment is needed to bring 1 liter of effluent to pH 5 after 48 hours of reaction?

2) Provide a robust assessment of the volume of reactants used per liter of treated fluid, the volume of any precipitates produced, and summarize the important changes in the fluid composition.

3) Test 2 changes in the process that would speed up the treatment and assess the practicality of those changes.

After the process had been running for several years, the company noticed that Ni++ and SeO3– were also present in the effluent.

4) Both of these solutes may adsorb onto HFO. Change the model to make Fe(OH)3(ppd) the product Fe-bearing phase by suppressing unwanted phases. Determine the quantity of these metals that would be adsorbed or co-precipitated with the waste products during your 2 day acid neutralization process using the information given below.

Ni++ = 10 ug/l

SeO3– = 10 ug/l

The surface_data  file used will be FeOH+.dat. You must remember to include the sorbate into the model when you execute. Explain what you think would happen with respect to adsorption if the process ran longer than just two days with reactants and products in contact.

Practical 5- Assessed Summary Practical. Acid waste with heavy metal contaminants: Treatment.