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UBC Theses and Dissertations

The recovery of copper from synthetic leach solutions with iron powder Hughes, Garry Maurice


Recent increases in the production of copper by acid-leaching techniques have depleted the supply of iron and de-tinned cans as sources of precipitant for copper from solution. Previous investigators of the iron cementation process have indicated that high purity iron powder, although more costly than detinned cans, has several properties which render it a potential precipitant of copper from leach solutions but few data have been published on the subject. The purpose of this thesis is to investigate the variables encountered in the cementation of copper with iron powder and to obtain data to substantiate indications that the iron consumption could be reduced and a higher grade cement copper could be produced which would compensate, at least in part, for the higher cost of the precipitant. A vertical column mounted on an inverted cone was used as the reaction vessel in the experiments. The pregnant solution was forced into the precipitator through the apex of the cone and the iron powder was added from the top of the column through a small diameter tube. The copper product was removed from the reaction vessel by the effluent solution and collected in a settling tank. Several series of experiments were conducted.to study the influence of variations in the velocity of solution flow through the precipitator, the concentrations of free acid ferrous and ferric ion in the pregnant solution, and the temperature of the pregnant solution on the iron consumption and the grade of the cement copper product. A velocity of solution flow in the column of approximately one centimeter per second was found to be suitable for iron powders retained on a 200 mesh screen. The capacity of the precipitator was reduced considerably with iron powder passing through a 200 mesh screen because iron of that size fraction was easily forced to overflow the precipitator before cementation.is complete. Neither temperature nor ferrous ion concentrations within the normal ranges of operation had any significant effect on the cementation process. Free acid concentrations up to twenty grams per liter were tested with no significant increase in iron consumption. The presence of ferric ion in solution during cementation enhanced the consumption of excess iron appreciably. Excess iron consumption was due to the reaction between metallic copper and ferric ions. The cupric ion produced in the reaction consumed additional iron by the normal cementation reaction. The reaction between metallic iron and ferric ions was not a major contributor to excess iron consumption. The consumption of ferric ion was not excessive at the beginning of experiments, when the surface area of metallic iron was at a maximum, but increased in approximate proportion to the increase in surface area, of metallic copper in the reaction vessel. Although the experiments were conducted with batch additions of iron the results indicated that the cone-column precipitator could be operated continuously by adding precipitant at a rate equal to its consumption. With continuous operation the contact between metallic copper and ferric ion was minimized which in turn reduced the iron consumption. The cement copper product of cementation from synthetic leach liquors with high purity iron powder was dried in alcohol and acetone and consistently contained more than ninety-five percent copper.

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