Leaching

Heap Leaching Copper Ore

Ranchers began its evaluation of the Bluebird Mine in late 1963. The property which included some 400 acres, adjoined one of the country’s leading producers – Inspiration Consolidated Copper Company. Such proximity led many to equate availability with undesirability. However, a relatively short period of exploration and metallurgical evaluation and a simultaneous assessment of other environmental elements led Ranchers to acquire the property and to expand its operation. The objective steady, continuous production, at a substantial level. The property was to become one of the first medium-sized copper mining operations to rely solely upon heap leaching as a means of production.

Development

Ranchers Exploration and Development Corporation obtained a 90-day option on the Bluebird property from Stovall Copper Company in January 1964. A 6,000 foot drilling program was initiated, and it was soon evident that the deposit consisted entirely of oxide ore. The economics of both vat and heap leaching were studied. Costs relating to mining, crushing, ore, waste and tailings handling, leaching, and recovery were examined closely. Leaching factors which received the most attention were acid consumption and costs and labor, power, and water costs. Since precipitation using iron was believed most feasible at the time, iron consumption and

Heap Leaching Economics

Expanded markets for copper in the past few years and a consequent search for new ore bodies have revitalized the widely known but seldom applied method of producing copper called heap leaching. This term should be differentiated from dump leaching in that the latter is applied to dumps of mixed oxide and sulfide ores (although either may predominate) that have been too low grade to beneficiate and have, therefore, been stripped off the higher grade underlying sulfide ores. Heap leaching is defined here as the process applied to oxide ores which have been mined solely for the purpose of leaching.

Although heap leaching does reduce capital expenditures, it also requires extensive test work and sound engineering to produce a successful operation. A company contemplating heap leaching must insist on a definite, well planned program of investigation. Adequate exploration is a necessity to assure that high acid consuming sections are not present in the ore body and test work must be done on drill cores to determine if acid attack on the host rock will result in physical degradation which would blind a leach heap. Items such as acid consumption, seepage and evaporation losses, leaching rates and anticipated ultimate recovery must be

Leaching of Copper by Fungi

Bacterial and fungal populations were observed in samples taken from the White Pine Copper Company tailing pond and mine, and isolates were prepared of the dominant species. The isolates were then screened for solubilization of copper from tailing, ore, and concentrate during incubation in a carbon and nitrogen supplying medium. Certain Penicillium fungi solubilized significant amounts of copper under neutral to slightly acidic conditions. Leaching apparently was accomplished by release into the medium of metabolites which chelated with the copper. The process was found to be highly dependent upon the medium and the concentration of copper in the source material.

Methods

The White Pine tailing disposal area covers about 1700 acres adjacent to the plant; the holding pond takes up about 150 acres. The samples were sealed in sterile one-half pint glass jars and refrigerated at 4° C. until they could be plated within the following 24 hours. After

leaching of copper sketch plan

vigorous shaking of the sample jar, one milliliter of fluid and suspended solids was pipetted into a sterile petri-dish and 25 milliliters of agar medium at 48° C. was added. The contents were mixed by swirling, and after the mixture hardened

Heap Leaching of Gold Ores in Northeastern Nevada

Heap leaching shows promise of being an attractive method for treating large tonnages of oxidized gold ores from the sedimentary beds of northeastern Nevada which are not economically amenable to treatment by conventional milling methods. The ores are unique, with the gold occurring as sub-micron particles in a porous host rock. The preliminary test work on representative samples from the region shows that a satisfactory recovery of the gold can be obtained by heap leaching the ores with cyanide at a relatively coarse size. Capital expenditures and operating costs for this method of treatment will be much less than conventional cyanide milling. The method could apply to deposits that are either too small or of too low a grade to warrant construction of a conventional mill, and for low grade portions of deposits where simultaneous operation of existing or proposed mills and heap leaching could increase treatment capacity and revenue from the operation at low additional capital and operating costs.

Technical and Economic Considerations of Heap Leaching

The technical and economic feasibility of applying the heap leaching process to the oxidized ores of northeastern Nevada offers great promise because of a number of favorable factors, including the following:

The nature of

Impermeable Dump Leaching Chemistry

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

Selection of a Leach Dump Test Area

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

Laboratory Extraction of Copper from Chalcocite by Roasting Reduction and Smelting

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

In Situ Leaching of Uranium

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 Oxide and Sulfide Copper Ores

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

Using Platinum Electrodes to Indicate Redox Potential

Platinum electrodes are not inert as originally thought to be. The reactivity of platinum electrodes can explain their erratic behavior in many electrochemical measurements of metallurgical interest, e.g., in flotation systems, streaming potential measurements, contact-angle measurements, and in leaching systems.

Experimental Procedure

A rotating platinum electrode was used in many of the measurements to study the effect of rotation on measured Eh values. The electrode made by the Pine Instrument Co., Grove City, Pennsylvania, consisted of a stainless steel rod with a platinum disc soldered to the end. It was covered with a teflon insulation along the sides, so that only the circular tip of the electrode was exposed to the solution. The platinum surface was brightened prior to its use on a metallurgical polishing wheel using alumina as an abrasive unless specified otherwise. The electrode was rotated with a Sargent synchronous motor at 350 rpm. The contact of the electrode with the external circuit was made by filling a notch at the top of the stainless steel shaft with mercury and by dipping a copper wire into the mercury pool. The performance of the rotating platinum electrode was compared with the performances of a Beckman type-Eh electrode and a

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