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PREFACE.

At its tenth regular session in 1913 the Utah Legislature provided for the establishment of a metallurgical research department in connection with the State school of mines of the University of Utah. As stated in the act providing for this department (Laws of Utah, 1913, ch. 102, sec. 2, pp. 199-200), the purposes of this research department have been to conduct experiments and research, either alone or in cooperation with the Federal Bureau of Mines and other agencies, with a view of finding ways and methods of profitably treating low-grade ores, of obtaining other information that shall have for its object the benefit of the mining industry and the utilization and conservation of the mineral resources of the State, and to publish and distribute bulletins and articles relating to the department and its work.

This act became effective in July, 1913. In January, 1914, the university made a working agreement with the Federal Bureau of Mines. By the terms of this agreement the work of the metallurgical research department is under the direction of metallurgists of the Bureau of Mines assigned to duty at the university and Salt Lake City. From January, 1914, to July, 1916, D. A. Lyon, metallurgist, was in charge of the work, assisted by O. C. Ralston and other members of the metallurgical staff of the bureau who were on duty at Salt Lake City.

As a part of the cooperative agreement, the University of Utah provides five metallurgical fellowships. The fellowships are awarded to graduates of colleges, preferably of mining schools, who have shown special aptitude for research investigations. Their employment extends over the entire 12 months.

Aside from O. C. Ralston, the experimenters mentioned in this bulletin in connection with the work were holders of these fellowships. Persons desiring further information regarding the cooperation between the university and the bureau are referred to Bulletin 157, Bureau of Mines, pages 9-11.

VAN. H. MANNING,

Director.

9

RECOVERY OF ZINC FROM LOW-GRADE AND

COMPLEX ORES.

By DORSEY A. LYON and OLIVER C. RALSTON.

INTRODUCTION.

Volatilization in retorts has been, until recently, the only commercial process of producing spelter, hence the zinc mine operators have had to meet the terms of the zinc smelters in regard to the following requirements: (1) Minimum percentage of zinc the ore must contain; (2) the chemical combination of the zinc in the ore; (3) the proportion present of those elements that interfere with the successful recovery of the zinc when the ore is retorted. In consequence of these requirements, only a comparatively small proportion of the zinc ores mined can be shipped directly to the smelters. ZINC ORES AND CONCENTRATES SUITED TO RETORT SMELTING.

Under normal conditions the low limit of zinc in ores suited to retort smelting is about 25 per cent for oxidized ores and about 35 per cent for sulphide ores. Consequently the ores or products suited to zinc smelting in retorts may be obtained from—

1. Zinc ores free from interfering elements.

2. Concentrates of zinc ores or of zinc-lead ores.

3. Concentrates of mixed and complex ores, containing gold, silver, lead, copper, zinc, etc.

Table 1, compiled from statistics published in the Mineral Resources of the United States for 1914, shows the principal zinc producing States and the kind of ores mined in them. The zinc produced from ore mined in Missouri, Kansas, Illinois, and Wisconsin comes from sulphide (blende), carbonate, and silicate of zinc; in other words, from class 1. The zinc produced in Utah and in Idaho, Montana, Colorado, and Nevada is largely from classes 2 and 3, or lead-zinc ores, the zinc being separated from the lead when the metallic minerals of the ore are separated from the worthless gangue by some form of mechanical concentration.

TABLE 1.-Production of spelter in the United States in 1914.

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As stated previously, and as will be shown later, a large part of the valuable mineral content of the ore is lost in effecting this concentration.

As a result of the other requirements that have to be met in zinc smelting, much zinc is lost in the mining and milling of zinc ore.

ZINC LOSSES IN MINING AND MILLING.

LOSSES IN MINING.

In mining the ore the zinc losses aggregate a large tonnage. These losses are due to several causes; for instance, in the average western lead mine the zinc ore remains as a shell around stopes from which the oxidized lead ores have been taken. In most mines the lateral extent of these shells is unknown, and as they generally carry too little metal to warrant mining at present, they are not removed. Later, the lead-ore stopes are filled with waste and the zinc in these surrounding shells is lost. Figure 1 shows the present sources of zinc and the ores not utilized.

LOSSES IN MILLING.

As only a small proportion of the zinc ores mined in the United States contains enough zinc to warrant direct smelting, separation of the valuable minerals from the gangue by some method of mechanical concentration is generally necessary.

For the sake of convenience, the concentrating processes used are considered herein in the following order:

1. Hydromechanical processes. 2. Electromechanical processes. (a) Electromagnetic,

(b) Electrostatic.

3. Flotation processes.

HYDROMECHANICAL PROCESSES.

In treating zinc ores by hydromechanical processes the object is to obtain a concentrate that, if necessary may afterwards be separated into a zinc product and a lead product, or into a zine product and a product that may contain lead, copper, gold, and silver, and is sent either to a lead or to a copper blast furnace.

As stated previously, a large proportion of the zinc and lead minerals is often lost in the tailing when any ore mined for its zinc or lead content is treated by hydromechanical concentration. As one of the functions of the Federal Bureau of Mines is to conduct investigations looking to the prevention of mineral waste, the bureau

Lyon, D. A., and Arentz, S. S., Losses of zinc in mining, milling and smelting: Trans. Am. Inst. Min. Eng., vol. 49, 1915, p. 799.

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