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Wet Autogenous Grinding in Tumbling Mills

The autogenous grinding method has been progressively employed in mineral dressing plants during the last 15 years. The term has been used with somewhat different meanings. In this paper the author will use it in the most restricted way, for processes where run-of-mine ore (rock) in one step is reduced to a grind product by the action of the ore itself without any other grinding media present. The pebble grinding process where the major part of the ore enters the mill as finely crushed product which is ground further with selected coarse ore pieces acting as grinding media, is not considered autogenous grinding. Processes where a minor amount extraneous media as steel balls is added to supplement an autogenous mill charge will be called semiautogenous.

Autogenous Grinding Mechanisms

Autogenous grinding is at present carried out in tumbling mills of the same types as used in ball mill grinding. The similarities in equipment and procedure have led to the commonly held assumption that the grinding mechanisms are the same in the two processes, with the coarse part of the ore charge taking over the function of the ball charge. This view is largely correct when considering pebble grinding, but the situation

Water in Fluorspar Flotation

Water has received little attention as a variable in flotation, even though it is a known fact that water hardness often has an adverse effect on purity and recovery, particularly on the flotation of non-metallic minerals. Because of this fact, process water used in some flotation plants is treated to reduce hardness to an acceptable level. In the laboratory, distilled water is usually used as the flotation medium in order to standardize conditions, whereas in flotation plants locally available water is used.

Laboratory flotation tests were run on a sample of the vein-type of ore used at Rosiclare Works in distilled water to which the commonly determined hardness components were added singly, in synthetic hard water and in a sample of Ohio River water. Tests also were run to determine means for counteracting the adverse effects of hard water. All flotation tests were run with pulps at pH 10 maintained with soda ash and at a temperature of 71°C in the rougher float, the conditions used at Rosiclare Works.

The following conclusions were drawn from this work. More soda ash was required to maintain pH in Ohio River water without ore than in distilled water without ore, the amount increasing with increasing

How to Increase Mill Performance Calculation Accuracy

Flotation processes contain disturbances which make material balance closures difficult to achieve. Lack of closure also arises from instrument errors. A portion of these problems can be overcome by proper equipment selection; the primary measurement installation and methods of initial data filtering are discussed below.

The Lagrange technique introduces multipliers to allow locating the extremes. The number of these “multiplier’s equals the number of constraint equations. The constraint equations are combined with an objective function to form the Lagrange Expression:

mill-performance-calculation-equation

The technique described here is based on that of Ripps. Flotation products, assay and mass flow measurements, are adjusted so as to close the flotation circuit material balance in accordance with a standard deviation weighting of the least squares criteria.

The objective function to be minimized using Lagrange Multipliers is:

mill-performance-calculation-equation-2

Where Mi = Adjusted mass flow or assay.
Mi’ = Measured mass flow or assay.
∅ = Objective function (minimize adjustments with weighting factor)
si² = Variance of measurement.
I = Number of measurements

The constraint equations are flotation circuit mass balances:

mill-performance-calculation-equation-3

The Lagrange Expression obtained is:

mill-performance-calculation-equation-4

Where

Ψj =

Chrysocolla Sulfidization and Flotation

Studies of sulfidization and flotation of chrysocolla involving the use of pH and sulfide ion instruments, a Zeta meter, microflotation techniques, and sensitive determinations of adsorbed sulfur have given new insight into the mechanism of the process.

Factors that affect the recovery of sulfidized chrysocolla by flotation appear to be the pH at which it is sulfidized, and certain alterations of the surface that occur during aging after sulfidization. Such aging results in increased recoveries.

After some preliminary experimentation, the following procedure was adopted for the sulfidization step in all experiments. Fresh solution was prepared for each series of three sulfidizations by dissolving a weighed quantity of 63 percent, fused sodium sulfide chips in distilled water, and diluting to one liter. Then 300 ml of this solution was placed in a beaker on a magnetic stirring plate, and electrodes for the determination of sulfide ion activity and pH were submerged in it. The pH was adjusted using hydrochloric acid, and it was maintained within a few thousandths of the desired value during the sulfidization by dropwise addition of either more HCl or more of the sodium sulfide solution. Acid was required during the first half while the basic sulfide solution was required

Stack Sampling Theory

In those few instances that total flow can be captured and also passed through a total volume measurement system, sampling procedures can be directed entirely to the train required to retain particulates and trap the gases or to the analytical instrumentation that may be used to monitor the gas stream. Such sampling conditions are usually limited to local exhaust vents, trap vents and the like; and are rarely applicable to large stacks involving a combustion process. The condition more frequently encountered in stack sampling is that of sampling a large mass of gases in such a way that the aliquot portion taken for analysis is actually representative of the mass. Concurrently that mass must be quantitated. The reliability of all stack sampling results is contingent on the successful capture of a representative sample as well as definition of the mass.

Sampling Methodology

The problems inherent in meeting that objective are related (1) to the purpose for which the samples are taken, and (2) to the physical conditions of stack gas flow. The first will guide the selection of sampling train and influence the selection of sampling head. The second will influence the procedures used to determine the volume of gas

Smelting of Military Electronic Scrap

Gold, silver, and platinum group metals are widely used in electronic and electrical components to provide long-term reliability, Construction of military equipment consumes the largest proportion of the precious metals used in the electronic and electrical industry. Due to obsolescence and damage, military electronics are presently being scrapped at the rate of about 15,000 tons per year. This scrap averages approximately 100 troy ounces of silver, 5 troy ounces of gold, 1 troy ounce of palladium, and lesser amounts of other precious metals per ton.

The high level of development and use of military electronic hardware that soon becomes obsolete assures an expanding supply of scrap electronic components from military sources.

Because of its highly variable and complex nature, military electronic scrap is practically impossible to sample and analyze for metal content. This fact coupled with the inflexibility of presently used scrap-processing methods, limits disposal to a relatively small part of the scrap that is now generated and has been accumulated by military reclamation operations. The Bureau of Mines is currently investigating alternative methods for efficient, low-cost recovery of the precious and base metals in diverse mixtures of military electronic scrap.

Leaching techniques were tried initially for processing the electronic scrap. Nitric acid

Parallel HydroCyclone Simulation

In order to simulate a grinding circuit, it is necessary to obtain valid mathematical models of the grinding mills and classifiers in the circuit. Several models of grinding mills have been proposed and models of cyclone classifiers are available.

Description of a Circuit

New feed enters an open circuit rod mill at a rate of 164 TPH (dry). The rod mill discharges to a sump, where the slurry joins with slurry that discharges from a ball mill in closed circuit with two Krebs 20″ cyclones in parallel. The contents of the sump are pumped to the cyclones. Cyclone underflow slurries are recycled to the ball mill, while overflow slurries are sent to flotation.

After careful reflection, it is apparent that with this feeding arrangement, feed solids will not split equally between the two cyclones. Cyclone 2 is treating a higher tonnage. Moreover, the characteristics of slurry flow lines within this feeding system are such that coarse solids probably tend to by-pass cyclone 1. Likely, cyclone 2 is treating more of the coarser feed solids. These preliminary considerations have important implications as we shall see.

Lynch Model of a Cyclone

The cyclone model developed by Lynch et. al. consists of a set

Selective Silver Processing Circuit

White Pine Copper Company, a subsidiary of Copper Range Company located in Michigan’s Upper Peninsula, mines a Pre-cambrian sedimentary deposit containing finely disseminated chalcocite, native copper and native silver. Silver occurs predominately in certain strata and presently provides a mill head averaging 0.25 ounces per ton.

Development of Silver Circuit

The silver contained in White Pine mill concentrates has intrigued metallurgists for years. First attempts to concentrate the silver in a profitable concentrate were made during the original pilot milling using gravity methods. A degree of concentration was realized, but grades and recoveries did not look promising.

The development of the selective silver circuit at White Pine from 1961 to date consisted of the following phases:

  1. Gravity Separation
  2. Laboratory Flotation Testing
  3. Pilot Plant Studies

In 1961 the Metallurgical Research Department began investigating various methods of extracting silver from mill concentrates. Laboratory tests were made on final concentrates using conventional gravity equipment such as tables, mineral jigs and hydraulic traps. This testing indicated a need for a classification step prior to any concentration. Cyclone testing of concentrates resulted in a rejection of the bulk of material in the overflow with some concentration of the native metals in the cyclone underflow due to differences

Vibrating Screens for Dewatering Coal

The performance test data presented in this paper is typical of the data used as the basis for one method of selecting the size of a dewaterizer and predicting the approximate average surface moisture content of the product after it has been through the dewatering process. It is important that this moisture content be determined because it becomes the basis for selecting the centrifugal or heat dryers which follow the dewaterizer in the process, or determining if the dewatered coal is “dry” enough to be loaded out without further dewatering.

The performance data presented here was gathered from four preparation plants which shall be identified as Plants 1, 2, 3 and 4. These plants utilize a total of thirteen dewaterizers listed on Figure 1 as numbers 1 through 13.

Plant 1 processes Ohio strip mine coal. The minus 6 inch raw coal is crushed to minus 1-¼ inch, cleaned in a pulsating launder and then sluiced to a triple deck 5′ x 14′ dewaterizer.

Plant 2 treats Illinois No. 6 and Illinois No. 5 strip mine coal. The minus 4 inch fraction is cleaned in two 6 cell jigs. The clean coal from the jigs is sluiced to two sizing and dewatering screens

Reinforced Plastic Equipment in Extraction Processes

Corrosion and product contamination have been difficult problems for extractive metallurgy industries in the U.S. because of the highly active chemicals used. During the past twelve years, other industries, particularly the chemical and paper segments, began to combat this problem with some degree of success using newer materials of construction, including reinforced plastics. These materials are made by combining a corrosion resistant thermosetting resin with a glass fiber reinforcing material and are used to construct hoods, stacks, blowers, tanks, towers, pipe, and equipment of the most complex configurations.

Applications of FRP Equipment

New applications of FRP (Fiberglass Reinforced Plastics) in extractive metallurgy have focused attention on the use of this type of equipment. Only a few years ago, the ore processing industry considered corrosion much like bad weather. Corrosion was costly, but there was little that could be done about it. Those materials of construction that would yield protection against a narrow range of corrosive compounds were alloys so expensive that in many cases they were economically unfeasible. As a result, conventional materials of construction such as carbon steel remained in use, despite high maintenance and repair costs and the frequent need for replacement.

The ability of various plastic resins to

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