Leaching

Factors Affecting Ore Leaching

This work defines and systematizes the physical factors of the problem of leaching and demonstrates for the first tine the utility of macropore volume, micropore volume., specific surface, pore size distribution and permeability as parameters of leaching based on a study of the recovery of uranium from the Top Black member of Chattanooga Shale.

A set of factors which govern the leaching of ores was defined and organized into a logical system based on the elements of leaching; namely, accessibility, physico-chemical interaction and transport. From this array a set of categories was chosen which permitted a regrouping as follows:

  1. Structural factors
  2. Fluid factors
  3. Factors common to fluid and structure
  4. Operational factors
  5. Chemical factors

Elements of Leaching

Accessibility is a vital element because interaction between the desired constituents and the leaching fluid cannot take place in the absence of contact.

The necessary sub-elements to establish contact between constituents and fluid are exposure and penetrability. Exposure is the opening up of the desired constituents and penetrability is the ability of the leaching fluid to penetrate to sites where desired constituents are exposed.

Exposure depends on volume, shape and location distributions of the values of a given mixture. Given two mixtures differing only in the volumes

How to Handle Coarse Ore in a CCD Thickener Circuit

The use of a series of thickeners for washing of the slime fraction of a leached ore is not uncommon in the uranium industry; however, few ore processing mills have used a thickener circuit for washing leached total ore. The common practice is to wash the sand fraction in classifiers and the slime fraction only in thickeners.

General Description of Circuit

The circuit utilized consists of eight wooden fir tanks, 60-ft diam by 12-ft deep, set in a line and staggered in elevation by approximately 3 ft. The washing water flows through the thickeners by gravity, while the ore pulp is pumped uphill from thickener to thickener. Adequate piping and pumping capacity are available so that any of the thickeners can be bypassed in the circuit.

The drive mechanisms used for these thickeners are driven by 3-hp motors. The mechanism is of the non-lifting type, and a torque arm is employed in the drive to indicate overloads. A pointer is attached to the torque arm and the load on the thickener is indicated on a dial attached to the drive.

The centerwell of the thickeners are approximately 10 ft in diam and 4-ft deep with a wooden launder attached to the inside

Oxided Copper Ore Leaching

The principal characteristics of the process is that when applied in medium or in great degree, it only needs unelaborated raw materials such as sodium chloride and calcium carbonate, or of medium elaboration, as sulphur which is found in large quantity in the North of Chili however, the system may be also applied to small copper plants provided that low cost sulphuric acid is available as a substitute for sulphur, that is, in those plants of small capacity where large additional installations are not needed for the regeneration of the leaching solution.

Leaching

The process requires the use of hydrochloric acid as leaching solution when treating copper ores, which may be produced in the plant itself. The operation is very simple, using sulphuric acid and NaCl as raw materials.

Our experiences have been done with solutions containing 36 grs. of hydrochloric acid per liter of solution in order to have a free acidity equivalent to 50 grs/liter of sulphuric acid which is the usual concentration of a leaching solution.

Hydrochloric solution has been prepared taking into account the stechiometric calculation of the reaction:

a). H2SO4 + 2 NaCl = 2 HCl + Na2SO4

The behavior of the leaching solution in front of copper specimens

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

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