Mineral Processing Engineering

A series of tests were run on fresh Becker drill samples from a drill hole in Kennecott’s Chino “J” dump, near Silver City, New Mexico, to obtain data on the leaching chemistry of a relatively impermeable sulfide copper waste dump. Vertical profiles were made of the moisture and soluble-salt content; the content of Fe+³, Fe+², Cu+², and H+ in the interstitial solutions; and the content (both total and non-water soluble) of iron, copper, and sulfur in the residues. Conclusions were drawn from these data concerning the leaching chemistry and hydrological nature of this dump.

This study was similar to a previous study conducted on other, more permeable leach dumps at Chino. Briefly, the conclusions of the first study are as follows:

1. Solutions are transported through major portions of more-or-less permeable dumps at variable and rather slow flow rates according to the permeability of the strata. Some short-circuiting of solutions through the dump, however, is indicated.
2. The oxidation and hydrolysis of iron-bearing solutions occurs in the upper 40 feet of these dumps. This phenomenon appears to be a result of bacterial, air, and ground-water oxidation of a near-surface zone of retained iron and copper salts. The cyclic addition of leach fluids and
   

Leaching of waste material at Kennecott’s Chino Mines Division at Santa Rita, New Mexico, has been accompanied by increasing difficulty in circulating leach solutions through the dumps. As a means of recognizing existing problems and considering alternative applications of the leaching concept, a leaching research program was proposed which could be applied to a specific, typical waste dump. Conclusions derived from the area could then be applied to other leaching areas at Chino.

Preliminary field data acquired through Becker drilling and logging determined the final configuration of facilities for a tritium tracer test which was conducted as a portion of the research program. The data have led to recognition of several leaching problems which were previously unknown, and which appear to be relatively common throughout Chino’s waste dumps. The data have also served as a positive basis for an evaluation of all testing designed to improve leaching and for decisions regarding future research goals and impact.

‘Chino’s J dump was selected as a leach dump test area for a leaching research program on the basis of four general characteristics:

1. The initial copper content of J dump was high and the apparent copper recovery through leaching is low. The current copper grade averages
   

In a broad sense, sulfide copper pyrometallurgy is a batch sequence in three separate vessels, i.e., reverberatory furnace to yield “matte copper,” a converter to produce “blister copper,” and another reverberatory furnace to produce fire-refined copper. Matte smelting is relatively unchanged since it became universal practice some 50 to 60 years ago. It is now serving wide range of smelter feed materials, but many concentrates ore not immediately amenable to the process. There may be an excess or deficiency of essential matte-forming, elements, so adjustments must be made to the furnace charge. When smelter feed carries a sufficient excess of sulfur, byproduct manufacturing of elemental sulfur or H2SO4, may be incorporated into the metallurgical flowsheet. At the other extreme, there arc abundant copper resources which lack sufficient sulfur and other elements to sustain the full chemistry involved in matte smelting. This necessitates adding sulfur to make the product fit the process, and usually none is recovered. From the standpoint of pollution alone, development of a smelting technique for low-sulfur concentrates not requiring the addition of sulfur would be a significant gain.

The Twin Cities Metallurgy Research Center has been engaged in a study to uncover a more direct pyrometallurgical process for

Sedimentary deposits contain an appreciable portion of the world’s supply of uranium. Predictions of nuclear fuel usage in the United States indicate that these reserves will have to be tapped if the domestic industry is to be the major supplier of fuels for the nuclear reactors. Techniques developed within the petroleum industry are a base on which to build economically attractive fluid mining processes for the recovery of these uranium values. The problems central to the success of such mining processes are the containment, control, and recovery of a narrow band of pregnant leach solution as it progresses from the point of injection to the point of production.

Occurrence of Uranium

Uranium is not a particularly rare element in the earth’s rust. Kirk and Othmer state that uranium is more abundant than cadmium, bismuth, mercury, and silver. About one-third of the world’s uranium reserves are in sedimentary deposits. To date, most of the uranium mining has been in arkosic sediments.

Sedimentary sandstones, generally, contain little uranium. Two notable exceptions to this rule are the carnotite deposits of the Western United States and Kazakstan in the Soviet Union. The carnotite deposits of the Western United States are irregular and scattered, and yet

Heap leaching is a simple means of recovering copper from oxide and oxide-sulfide ores. Although this method requires relatively low capital investment, it suffers from low copper recoveries and relatively high acid consumption. The objectives of this study were (1) to determine what factors influence these shortcomings, and (2) to establish a basis of correlation between laboratory and field testing.

The principal methods of leaching copper ores at the present time are heap, dump, in-place, and vat. A number of references are presented in the bibliography on the theoretical and practical aspects of these methods.

In the heap-leaching method, crushed or uncrushed oxidized copper ore is placed on a prepared drainage pad. Acid leach solutions are distributed over the top of the heap, caused to percolate downward through the ore bed by gravity, and are drained from its base. The leach duration is generally a matter of a few months.

Dump leaching is used to recover copper from very low-grade oxide-sulfide pit-waste materials. Here again, leach solutions are percolated downward through a heap. However, in this method, little or no acid is added to the leach liquors prepared drainage pads are not used and the leaching cycle is generally measured in terms of