A process has been developed to remove copper from wastewater generated during e

Question

A process has been developed to remove copper from wastewater generated during electroplating. The process involves adding scrap aluminum to an acidic solution containing dissolved copper ions, which precipitate as metallic copper, Cu degree (s), and can be removed by settling and filtration. The relevant reaction can be written as follows: 3Cu^2+ + 2Al degree (s) 3Cu degree (s) + 2A1^3+ Standard free energies of formation for the ionic species in the reaction at delta G degree_f = 65.5 kJ/mol for Cu^2+ and delta G degree_f = -489.4 KJ/mol for Al^2+. If the wastewater initially has 350 mg/L Cu2+ and no dissolved aluminum and is dosed with 180 mg/L. aluminum scraps and the above reaction procedes to equilibrium, what will be final concentration of cu^2+, Al^3+, as well as the Cu degree (s) and Al degree (s), also expressed in moles per liter.

Explanation / Answer

delta G for a reaction is delta G f(products)- delta G f (reactants)

= 2 x -489.4kJ/mol - (3 x 65.5 kJ/mol)

= -1175.3 kJ

delta G = -RTlnKeq

-1175300 = -8.314 x 298 x ln Keq

ln Keq = 474.3

Keq = 1.04 x 10204

Since the K eq is very high all copper will be removed from solution to the extent of Aluminium added

180 mg Al is 180/26.9 = 6.69 mM/L

350 mg Cu is 350/63.5 = 5.511 mM/L

3 moles of copper reacts with 2 moles of Al

5.511 mmoles of copper needs 3.67 mmoles of Al

Since Al is in excess all Cu2+ is removed from solution and Copper metal formed is 350 mg/L or 5.511mM/L; Cu2+ is 0

Aluminium as Al3+ is 3.67 mM/L aluminium metal is 6.69-3.67 = 3.016 mM/L

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