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Variation of Point of Zero Charge of Oxide Minerals as a Function of Aging Time in Water

In recent years there has been a considerable amount of research work done relative to the effect of pretreatment and aging in water on the surface properties of both simple metal oxides and more complex oxides such as the silicate minerals.

The present paper investigates the change of point of zero charge (PZC) of a number of simple oxides and several complex oxides as a function of aging time in water. In some cases acid pretreatment of minerals was performed. However, in most cases the minerals were not acid pretreated. In several systems pH change as a function of aging time in water was monitored.

Experimental

Pure mineral specimens were prepared for study by first hand-picking best appearing specimens and reducing them in particle size in either an agate mortar and pestle or, in the case of asbestiform minerals, in a tungsten carbide pica mill. Next, the minerals were separated into plus and minus 325 mesh fractions. The latter were retained for experimentation. In addition to naturally occurring minerals, synthetic Al2O3 (Linde A) was also studied. In all cases minerals without further treatment were stored in plastic vials.

Electrophoretic mobility studies were performed with a commercially available microelectrophoresis apparatus, the zeta meter.

Installation and Effect of an Underground Crushing and Conveying System

Meramec Mining Company, a joint venture by Bethlehem Steel Corporation and St. Joe Minerals Corporation, is engaged in the mining, concentrating, and pelletizing of iron ore from the Pea Ridge Mine located near Sullivan, Missouri, about 70 miles southwest of St. Louis.

Crusher and Conveyor System Layout

The heart of this system is a 42-inch gyratory crusher on the 2475-foot level. The manufacturer agreed to split the top shell, making it possible to lower such a large crusher down No. 1 shaft. This is fed by a 72-inch wide by 20-foot long reciprocating feeder which empties the ore pass system from the four Swedish-style dumps above. Liner wear in the reciprocating feeder is monitored from outside with an ultrasonic thickness tester, and replacement is scheduled according to this ultrasonically measured thickness. The crusher drops ore into a small surge bin and then onto a 60-inch wide by 16-foot long vibrating feeder with a 4-foot long grizzly end which in turn feeds the conveyor. Feed rate is monitored by the crusher operator via closed circuit TV.

The operator’s control room houses the main control panel which by means of push buttons, indicator lights, alarm panels, motor ammeters, and closed circuit television

Surface Oxidation of Chalcocite

For sulfide minerals, the presence of dissolved oxygen in the water phase is an influencing factor for separation by flotation, Klassen and Mokrousov distinguish three stages of oxygen adsorption; namely, reversible adsorption, activated adsorption and, finally, surface oxidation. While contraversial, limited adsorption of oxygen is believed to improve the interfacial reactivity between collector and mineral. Intensive surface oxidation of sulfide minerals usually results in unsatisfactory flotation with collectors of the xanthate type.

Products of Oxidation

Eadington and Prosser state that the principal products of oxidation of lead sulfide by oxygen dissolved in water are sulfur, basic lead thiosulfate, some polythionate and, ultimately, lead sulfate. These investigators believe that the reaction proceeds by at least four stages; (1) an induction period, the length of which depends on the non-stoichiometry of the lead sulfide, (2) a short acceleratory period, (3) a period of steady rate of oxidation, in which the rate depends on non-stoichiometry and irradiation, and, (4) a period of retardation by lead sulfate.

Sharply contrasting is the general lack of information with regard to the oxidation products on the surface of sulfide minerals. Leja, Little and Poling state that PbS2O3 is the original oxidation product present on the surface of lead

Use of Simulation Models to Design, Optimization and Control of Wet Grinding Circuits

Mineral comminution is an important and expensive industrial process and modern comminution circuits are complex. There is considerable economic incentive to optimise circuit design and performance and to operate circuits at maximum efficiency, and these aims may be achieved by setting up mathematical models of the volts in a circuit on a digital computer and studying the behavior of simulated circuits.

Mathematical Model of Comminution

For many years attempts were made to develop a mathematical description of the comminution process in terms of an energy-size reduction relationship. This was suitable for some purposes but was inadequate for simulation work in that the complete size distribution was not considered. In 1948 Epstein developed a statistical model of a breakage process which depended on two basic functions, Pn (y), the probability of breakage of a piece of size y in the nth step of a breakage process, and F(x,y), the distribution by weight of particles of size x less than or equal to y arising from breakage of-a unit mass of size y.

Broadbent and Calcott used the concepts of breakage, (B) , and selection, (S), functions in place of the distribution and probability functions of Epstein and wrote the equation

p

Reclamation of Mineral Milling Wastes

The Administration’s proposed Mined Areas Protection Act suggests that each State in the United States be encouraged to develop within 2 years its own program for the regulation of mining activities. In the event individual States prepare inadequate proposals, Federal regulations would be applied. By implementation of this law, land, air and water adjacent to mining operations would be protected and regulatory inconsistencies between the States would be eliminated. The preplanning for waste disposal occasioned by this, Act would ensure that mined land protection would be considered as an integral part of the mining and processing industry.

The U.S. Bureau of Mines has been conducting research on the utilization and stabilization of mineral wastes since passage of the Solid Waste Disposal, Act of 1965. Considerable research has been done on methods of producing plaster and wallboard from waste gypsum from the phosphate industry; rock wool from fly ash and other mineral- wastes; concrete and ceramic products from various tailings and slags; artificial soils from tailings and sewage sludge or municipal refuse compost; and bricks from many waste sources. Research on the stabilization of mining and milling wastes has been done for elimination of air and water pollution, improvement of the appearance

Pelletizing Ore Mixtures

In 1965 Hoogovens was looking for additional capacity for burden preparation in the order of 2.5 to 3 million metric tons per annum of some kind of optimal blast furnace ore feed. In principle four solutions offered themselves for further investigation:

  1. purchase of screened ore and/or run of mine ores with the provision of a corresponding ore screening capacity on the blast furnace site;
  2. manufacture of sinter;
  3. purchase of pellets;
  4. manufacture of pellets.

Selection of the equipment parts

A survey of existing installations revealed a great number of alternative solutions out of which a choice had to be made:

a. mixing of the ores from bins or the use of mixing beds;
b. dry or wet grinding before or after mixing;
c. open or closed grinding;
d. disc or drum balling;
e. grate kiln or straight grate installations for the induration.

The choosing was done comparing the results of numerous tests, ordered by Hoogovens at various pilot stations.

When mixing of the ores before grinding it could be feared that the soft ores would be overground and the hard ores stay too coarse.

In practice, however, the grindability of rich ores does not differ much, so that a good narrow screen analysis of the ground ore can be

Particle Size Distribution of Grinding Mill Products

This report briefly reviews the essential features of moment analysis and describes extension of this method to size reduction by ball mill grinding.

Method of Analysis of Size Distribution Data

Size analyses of mineral products are usually made by screening with a set of sieves having mean apertures arranged in the Tyler scale, which is a geometric progression with a constant ratio equal to the square root of two. For this reason it is convenient to represent particle size as a logarithmic function of the particle diameter

X = l/log√s log(d/do)……………………………………………………(1)

where s = l/√2
d = particle diameter,
and do = reference diameter.

The variable, x, may be defined as the logarithm to the base s of the ratio of the particle diameter to the reference diameter, d. The inverse of the transformation given in equation 1 is given by equation 2:

d = dosx…………………………………………………………………(2)

The reference diameter may be any convenient standard length such as the mean aperture of the largest standard sieve used in the screen analyses.

The kth moment about an arbitrary axis, xo for a set of size distribution data is defined by equation 3:

grinding-mill-products-equation

where yi is the weight fraction

Oxygen Consumption in Dump Leaching

Column leach studies of a low-grade porphyry copper ore were made. The technique used involved alternating oxygen absorption and copper leach cycles. The leach solution was displaced from the column with oxygen. The volume of oxygen reacting with the ore was measured with a gas burette. The copper released as a result of exposure to oxygen was correlated with the oxygen uptake.

The Experimental Method

Reactions were carried out in plastic columns in which leach cycles were alternated with oxygen cycles. Samples of the leach solutions were taken periodically and the volume of oxygen reacted was measured for each cycle.

The leach columns were constructed from 6 ft. cast acrylic tubes having a 5 inch outside diameter and a 4.5 inch inside diameter. An acrylic lid was used to seal the columns, using a rubber O-ring as a gasket. This arrangement gave a satisfactory gas seal. The leach solution was drawn from the bottom of the columns, passed through a sampling chamber and returned to the top with a centrifugal pump.

The material leached in this research was a porphyry copper ore, hand selected from the Bingham Canyon Mine of the Kennecott Copper Corporation, Utah Division. The material was crushed and sized

Aqueous Oxidation of Molybdenite in Chalcopyrite Concentrates

Molybdenite and chalcopyrite are two often-associated minerals. In Quebec, the Gaspe Copper Company, a subsidiary of the Noranda group, currently operates a molybdenite flotation circuit to recover a one percent trace of this mineral in the chalcopyrite concentrate. The low levels of molybdenite preclude the use of flotation to remove molybdenum directly from the ore while scavenging of chalcopyrite concentrate for molybdenite yields a concentrate of the latter of somewhat inadequate quality. Such a situation could possibly best be solved by hydrometallurgical means, if molybdenite could be leached selectively from the chalcopyrite concentrate.

Experimental Set-Up

In order to perform solubility measurements simultaneously with analyses of the solution for dissolved molybdenum and copper, an autoclave from Autoclave Engineer, PA, has been equipped with a liquid sampling system designed to operate at the pressure and temperature prevailing in the autoclave. A sampling cycle would remove and cooled down a 5 cc sample for chemical analysis and send a 0.2 cc sample to a chromatograph, following flash evaporation and water stripping on a drierite column.

Results and Discussion

In order to verify the accuracy of the present technique for solubility measurements, solubility data for oxygen, nitrogen, carbon monoxide have been determined as a

Optimizing Grinding and Regrinding Capacity in Mill Design

The intent of this paper is to try to answer the complex question: “How much grinding capacity should be designed into a new mining – milling project?” Much work has been devoted to the technical aspects of grinding, the “how” of grinding. But, in the writers’ opinion, the economically important subject of optimizing grinding capacity in mill design has not received the attention it deserves, at least not in published literature.

Optimizing Primary Grinding Capacity

The relation of fineness of grind to the degree of liberation of the valuable minerals from the gangue is certainly a factor to be considered in optimizing the primary grind. This largely determines the grind-recovery curve and the point of maximum recovery, which is normally at a very fine grind. However, it is obviously not the only factor to be considered. How closely the optimum grind actually approaches the maximum-recovery grind depends on the following factors:

  1. Grindability
  2. Operating Cost Factors
  3. Capital Cost Factors
  4. Product Value
  5. Mining Factors

In any plant, considerable fluctuation normally occurs in grade of ore, grindability and fineness of dissemination. However, since grinding is usually by far the most expensive unit operation in a concentrator, the grinding capacity is normally designed for average rather

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