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PRECIPITATION BY GASCARBON MONOXIDE

RENDY HARRISTA

3334091122

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OUTLINE

1. Introduction

2. Reduction Reactions of Metal Ions with CarbonMonoxide in Aqueous Solutions

3. Basic Theory

4. Reduction of Silver Acetate by CarbonMonoxide

5. Reduction of Cupric Salts in Aqueous Solutionsby Carbon Monoxide

6. Application

7. References

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INTRODUCTION

The process of forming a precipitate from a solution

Precipitation by gas Hydrogen

Precipitation by gas Carbon Monoxide

Precipitation by gas Sulphur Dioxide

Precipitation by gas Hyrogen Sulphate

PRECIPITATION

KINDS of PRECIPITATION by GAS

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Reduction Reactions of Metal Ionswith Carbon Monoxide in Aqueous

SolutionsA number of metals have been successfully producedfrom aqueous solution when subjected to carbonmonoxide. The severity of the conditions necessary forthe reactions to proceed at reasonable rates may vary from

atmospheric CO pressure and room temperature.

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Basic Theory

The reduction of a divalent metal ion in aqueous solution bycarbon monoxide takes place according to the equation:

M2+ + CO + H2OM + CO2 + 2H+

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CARBON MONOXIDE REDUCTIONOF AQUEOUS SILVER ACETATE

Rate of Carbon Monoxide Reduction of Silver(I) Earlyexperiments demonstrated that at low pH the reduction ofAgClO4 solutions was very slow even at temperatures of175C and CO pressures of 20 atm. When the solutions

were buffered with NaOAc and HOAc, however, the rateswere readily measured under much milder conditions bythe pressure-drop method.

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CONT . . .

The observed kinetics are consistent with the formation of intermediatecomplexes by the insertion of a carbon monoxide molecule between asilver ion and a co-ordinated oxygen-donating base according to thefollowing mechanism:

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CONT. . . Chemistry and Stoichiometry of the

ReactionWhen dissolved silver undergoes reductionby carbon

monoxide in acid solution the reaction

products are silvermetal and carbon dioxide according to the

reaction:

The Ag(I)-CO-C02 stoichiometry of reaction was

examined at several temperatures by analyzing liquid andgas samples taken after about 50-60 % reaction hadoccurred. Solution composition and experimentalconditions that gave relatively fast reduction rates were

selected. The results of these measurements, assummarized in Table, agree within 10% with thestoichiometry represented by reaction

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Effect of Carbon Monoxide Pressure

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Effect of Acetic Acid

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Effect of Temperature

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THE REDUCTION OF CUPRIC SALTS INAQUEOUS SOLUTIONS BY CARBONMONOXIDE

Rate of Carbon Monoxide Reduction of Cu(II)

Recently McAndrew and' Peters began a study of thekinetics of the Cu(II)-CO reduction reaction using the

pressure-drop technique. The pressure time curves obtained in these studies showed pressure minimal and wereinterpreted as representing two stages - of reduction, the first

being from Cu(II) to Cu(I) which follows a stoichiometryconsistent with the overall reaction

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CONT . . .

And a second stage involving either further reduction to metal orhydrolysis to Cu20 according to the reactions

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Effect of Carbon Monoxide Pressure

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Effect of Increaseing Carbon MonoxidePressure

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APPLICATION

Recovery of copper, by copper smelters slag at Ghatsila(Bihar) and Khetri (Rajasthan), India.

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REFERENCES

McAndrew, R.T., and Peters, E., "The Displacement of Silverfrom Acid Solutionr by Carbon Monoxide",XVIIIth Congress,International Union of Pure and Applied Chemistry, Montreal,1961.

Habashi, F. 1980. Extractive Metallurgy, volume 2,Gordonand Breach, New York and London.

J . J . Byerley, and E. Peters, "The Reduction of Cupric Salts i nAqueous Solutions by Carbon Monoxide", to be published i n

Metallurgical Society Conferences, Hydrometallurgy:Proceedings of a Symposium sponsored by the MetallurgicalSociety of A.I.M.E., Annual Meeting, February 24 - March 1,

1963, Dallas, Texas.

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THANK YOU

ANY QUESTION ? ? ?

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