LOSSES IN COPPER-SMELTER SLAGS

A study of metal losses in copper smelters of the Southwest has been completed at the Southwest experiment station at Tucson, Ariz. Data were collected on the conditions existing at the various smelters, the various modes of operation, the character of ores charged, and the fluxes employed. With this information in hand the bureau's metallurgists were enabled to make a close comparison of the results being obtained in the different smelters. The object of this study was to determine as closely as possible the causes of losses of metal into copper slags, in smelting low-grade refractory ores which in addition to copper carry one or more of other metals-gold, silver, lead, and zinc.

METALLURGY-WET PROCESSES

RESEARCH IN ORE DRESSING

A survey of the status of research in ore dressing in the United States, Ontario, and British Columbia, made by the milling committee of the American Institute of Mining and Metallurgical Engineers and the Bureau of Mines, reveals that considerable experimentation is being conducted at great cost to the mining industry, but that this research is in general poorly coordinated. A report made to the above-named agencies states that, although companies are adequately taking care of routine tests and the mechanical features involved in their own operations, no comprehensive study of the fundamental principles of ore reduction is now in progress or contemplated.

Although the report relates primarily to the reduction and concentration of ores and nonmetallic minerals, it contains short sections on coal and clay. The mechanical handling that these minerals undergo is considered as "dressing," so that ore dressing includes metallic and nonmetallic minerals.

The necessity for this survey was brought to the attention of the Bureau of Mines by the chairman of the milling committee of the American Institute of Mining and Metallurgical Engineers. The survey, which has been carried on under the direction of the Bureau of Mines, was made possible by the cooperation of the University of California in lending a secretary to the committee and by the cooperation of the mining department of the Massachusetts Institute of Technology in supplying suitable quarters and assistance, together with the hearty support of the faculty. It is the desire of the committee on milling methods that all interested in this subject lend their aid to the committee, especially by giving their opinion of the needs of the industry and by calling attention to problems requiring solution that have not been mentioned in this report. Correspondence may be addressed to United States Bureau of Mines, University of Utah, Salt Lake City, Utah. The study gives a broad basis for systematic research on the fundamentals of ore dressing.

LEACHING OF COPPER ORES

Technical Paper 312, Leaching Nonsulphide Copper Ores with Sulphur Dioxide, was recently published by the bureau. This process

was devised to provide a cheap and efficient method for treating the so-called "porphyry" copper ores of the Southwest which generally contain both "sulphide" and "nonsulphide" copper minerals. These minerals are mixed in such proportions that they can be satisfactorily treated only by a method that will concurrently recover both the sulphide copper and the nonsulphide copper. The importance of this process may be judged by the fact that more than one-half of the copper produced in a recent year in Arizona and New Mexico, amounting in value to $106,000,000, came from the so-called " porphyry" low-grade deposits.

It is thought by the Bureau of Mines investigators that the sulphur dioxide leaching process, developed by the Southwest experiment station of the bureau, in cooperation with the Miami Copper Co. and the Arizona Copper Co., is suitable and commercially available for a wide range of the ores above described.

SELECTIVE FLOTATION OF COPPER MINERALS

A study of methods of selective flotation as applied to heavy sulphide ores, with particular attention to separation of copper sulphides from pyrite, is being undertaken at the Southwest experiment station, Tucson, Ariz. The effects of different oils in varying proportions and concentrations in neutral, basic, and acid solutions will be studied, and the effect of various chemicals on the separation will be determined.

PURIFICATION OF COPPER SULPHATE SOLUTIONS

Experimental work on the purification of copper sulphate solutions from the leaching of low-grade oxidized ores is being continued at the Pacific experiment station, at Berkeley, Calif. Attention has recently been chiefly given to the removal of ferrous and ferric iron from such solutions, together with any aluminum present.

RECOVERY OF ZINC IN LEACHING COMPLEX ORES

Leaching with sulphuric acid oxidized ore that contained a large amount of zinc sulphate has, heretofore, been considered impossible. Research work performed at the intermountain experiment station has shown that: (1) By treating the oxidized ores with sulphides, the mixtures may be made self-supporting as to acid when the zinc sulphate formed is electrolyzed; (2) by the use of leach liquors of proper acid strength throughout the process, any trouble due to soluble silica may be avoided. Practically, this means that the present hydrometallurgical process for the treatment of zinc sulphide ores may be enlarged in its scope to include ores of almost any class, and that much zine that is now run into smelter slags at a great cost may be saved.

PROCESS FOR PREPARING FERRIC SALTS

Laboratory research on the preparation of ferric salts has been successfully completed at the Pacific experiment station, Berkeley, Calif. The object was to prepare solutions of ferric salts suitable for use in hydrometallurgical treatment of complex ores, by

some simple method that could be cheaply applied in commercial treatment. The process worked out by the bureau involves the conversion of impure ferrous sulphate to ferric form by bubbling air containing sulphur dioxide gas through the solution. Conditions and factors that disturb the chemical reactions have been carefully determined, and the process can now be controlled with certainty. The study has shown that the use of pressure does not speed up the reaction sufficiently to be of commercial importance. The application of this process to the treatment of ores is being followed up by the Intermountain experiment station.

IDAHO METALLURGICAL PROBLEMS

An improved type of hydraulic classifier has been developed in the work on ore-classification problems in treating complex lead-zinc ores of the Coeur d'Alene and other mining districts of Idaho. This work was done at Moscow, Idaho, where the Bureau of Mines maintains field offices in cooperation with the University of Idaho. This new classifier is believed to be more efficient than any now in use, and to represent a distinct advance in metallurgical treatment. The new classifier has been tried out on a commercial scale in one of the mills, where it greatly improved the grade of classification. It has already been adopted for use in two of the large mills of the district and in one mill in Alaska. It is believed that table concentrations will be greatly improved when the feed to tables is properly classified. Also, with this type of classification, apparently galena and sphalerite may be separated on tables into marketable products, and much of the fine grinding and difficult flotation treatment of complex lead-zinc ores may be eliminated. Intense interest in the trial has been manifested throughout the district, and many other mills are expected to install this device and thus improve their products and conserve mineral now lost in the reject.

A study of the treatment of dry gold-silver ores of southern Idaho is also being made, and one on the metallurgical problems involved in the treatment of gold-silver ores from Bay Horse mine and ore from the Azurite mine in southern Idaho, is about to be undertaken.

CERAMICS AND NONMETALLICS

BURNING PROBLEMS OF INDUSTRIAL KILNS

Important fuel economies in the operation of industrial kilns manufacturing brick, tile, and other heavy clay products have been made possible as the result of a study of the burning problems of such kilns, made by the Bureau of Mines in cooperation with the four heavy clay products associations. Engineers of the bureau traveled on a specially equipped laboratory car and studied actual firing conditions at typical plants that produced common brick, face brick, paving brick, and hollow building-tile. The practical demonstrations of the bureau engineers resulted generally in a considerable reduction of time of burning and in amount of fuel consumed, and improvement in the quality of the manufactured product. The results of this investigation have been incorporated in a report on "The Burning Problems of Industrial Kilns," published by the four

heavy-clay products associations-the National Paving Brick Manufacturers Assoc., the Common Brick Manufacturers Assoc., the American Face Brick Assoc., and the Hollow Building Tile Assoc. Similar studies have also been conducted in cooperation with the American Refractories Assoc. Such plant research makes a definite and practical contribution to the movement for conservation of fuel.

OXIDATION OF CLAYS IN FIRING

Research work was completed on the effects of the absorption of sulphur gases by ferric oxide in clays, when a clay ware is being burned in the kiln. The changes in the nature and amount of sulphur absorbed at different temperatures were accurately determined. It was found that with increase in temperature up to 450° C. about half of the ferric oxide changes to ferric sulphate, a soluble salt that may cause scumming. At high temperatures some of this ferric sulphate and most of the remaining iron is combined with sulphur in an insoluble form.

This work is part of a general study of the oxidizing effects of various impurities present in different clays, and coals used for fuel, on the quality of the ware, to determine what substances are responsible for bloating, shrinkage, warping, and discoloration.

MINERAL GRINDING STUDIES

The grinding of flint for ceramic uses is a difficult problem on account of the great toughness and resistance to abrasion of the material. Heating the flint before grinding makes the process easier. Investigators at the Nonmetallic Minerals experiment station at New Brunswick, N. J., will test the efficiency of combined heating and quenching. The method may be extended to other minerals.

UTILIZATION OF ANHYDRITE

Anhydrite, which occurs in considerable quantities at some gypsum mines, is now practically waste. The Bureau of Mines is trying to determine the amount of anhydrite available at various plants and the possibility of finding useful applications for it in industry; for example, as a substitute for gypsum as a retarder in Portland cement. This work is being done at the Nonmetallic Minerals station at New Brunswick, N. J.

MINERAL FILLERS

Investigation of the availability of certain minerals for use as fillers, their physical and chemical characteristics, and their adaptability to commercial uses, is being continued. The South has extensive deposits of clay, ochers, bauxite, talc, and graphite, which may be available as mineral fillers.

Mineral fillers are pulverized nonmetallic minerals used to give body to various manufactured articles. Kaolin, whiting, chalk, ground limestone and marble, silica, ocher, mica, talc, barite, slate flour, graphite, and diatomaceous earth are the chief mineral fillers. Fillers are used in many industries, chiefly for the following products: Paper, wallpaper, prepared roofings, rubber, paint, linoleum,

oilcloth, foundry facing, plastic cements, oxychloride cement, artificial stone, polishes and scouring compounds, matches, dressing and dusting powders, various textile products. such as window-shade cloth, and phonograph records.

CONVERSION OF CLAY TO ALUMINUM SULPHATE

Large-scale tests have been completed on the new process devised by the bureau to prepare aluminum sulphate from alunite. In these tests, using a unit charge of 1 ton, the results confirm the conclusions drawn from earlier 100-pound runs, that by a preliminary treatment with acid, removal of the iron to a mere trace and elimination of most of the potash is practicable. This leaves an iron-free residue. which can be worked up into aluminum sulphate. Alunite consists of aluminum and potassium sulphates, with iron and other minerals present as impurities.

Experiments are being continued to determine the best conditions of temperature, pressure, and other factors for maximum efficiency of the process. The process when perfected will, it is believed, provide a much-needed, simple. and cheap method for manufacture of pure alum and aluminum salts from impure clays. Under present methods the pure salts cost about twice as much as impure salts.

REFRACTORIES

DOLOMITE FOR REFRACTORIES

Research work on the utilization of dolomite in refractories is being continued at the Ceramic experiment station, Columbus, Ohio. The main problem being studied is to combine the lime in the dolomite so that it will be nonslaking and at the same time will hold up the refractories, thereby rendering available abundant deposits of dolomite for use as a basic refractory. Work previously done by the Bureau of Mines on different fluxes for rendering dolomite refractories nonslaking indicated that by careful selection and preparation refractory bricks could be made, one of the best fluxes tried being alumina-iron flux. As the result of more recent work, a composition has been found which, when compounded with the proper binder and burned after a given procedure, produces a strong, nonslaking brick of high refractoriness. The bricks are satisfactory in every respect, except that uniform shrinkage has not been completely attained. During the coming year bricks will be produced and tested in the industry.

POWER-PLANT REFRACTORIES

A cooperative agreement has been made with a group of large central power-plant operators, represented by C. A. Hirshfield, of Detroit, to make a survey of present conditions relating to the use of power-plant refractories.

With the present high ratings at which boiler plants are being operated and the increasing use of pulverized coal with its attending high temperatures, the refractories now available for lining boiler furnaces are proving inadequate. Characteristics of refractories now