Mineral Processing Engineering

How to Design Grinding Mills for Mechanical Reliability

In the early mills, the material was ground in batches, the mills being charged and discharged through doors in the shell. The shell was supported by means of solid trunnion shafts resting in plain bearings and the drive was accomplished through one of these shafts. In some later batch mills, the mill shell was supported on rollers which were also used to drive the mill. At an early stage, continuous operation was made possible by feeding and discharging the mill through hollow trunnions, the method still in most widespread use.

Scale Effect

The effect of size on the design of grinding mills can be Illustrated by two very simple excursions into dimensional analysis and strength of materials.

In practice, the unit loads on the bearings of small mills are relatively low in magnitude. However the effect of increasing size is such that in mills which were considered large 5 to 10 years ago the bearing pressures (in conjunction with other factors to be discussed later) were approaching a critical level. Unfortunately, the requirements for material flow through the trunnions dictate their geometry to some extent so that the only methods available for relief of the situation are either to increase the

By Jorge|2019-04-19T10:53:17-04:00April 17th, 2019|Categories: Grinding|Tags: 972|Comments Off

Design Criteria of Mined Land Reclamation

While the late 1960’s are known as the years of the public recognition of impending environmental crises, the 1970’s will be known as the decade of public concern for improving the quality of that environment. One of the present major environmental concerns is the temporary disturbance resulting from coal surface or open cast mining.

Certainly the economic aspect is of primary concern as a company contemplates mining in a specific coal field. However, of equal significance today are the aesthetic and social implications to the community, with the aesthetic being the most obvious and important concern to the general public. This is especially true as greater expanses of topography and its vegetation are disturbed. It is granted that other objections to surface mining of a specific land unit may be given (e.g. changing land-use patterns, fears of decreased tax valuation, effects on adjacent property, etc.), but the temporary disruption of the natural environment and long-standing land-use patterns, changed plant communities, modified topographical features and a short-term biological desert are unsightly conditions degrading to man’s sensibilities and his aesthetic values.

The design criteria of reclaiming mined lands should include those parameters essential to insuring the restoration of the physical, chemical and biological aspects

By Jorge|2019-04-19T10:53:30-04:00April 17th, 2019|Categories: Environment & Tailings|Tags: 972|Comments Off

Engineering & Chemical – Quality Control of Metallurgical Wastes

There are generally four operational units in Butte: underground mines, open pit mine, concentrator and precipitation plant. As with copper production, the waste water systems for all units are interrelated. Acidic mine water is pumped up the Kelley shaft and distributed on leach dumps. Major waste water discharges from the Butte operations include: about 4400 gallons per minute (gpm) acidic water from the copper precipitate plant, about 8200 gpm alkaline water from the concentrator and some spills (including tailings from the concentrator circuit).

Silver Bow Creek has a present water use classification for industrial waste and has been used as such for over 70 years. At Warm Springs the name of this stream is the Clark Fork River where the classification is presently “CD2”. Governmental agencies have indicated that the CD2 classification should be raised to BD1. The letter designations for these classifications represent the intended water use for the stream in question: CD2-Bathing, swimming and recreation, growth and marginal propagation of salmonid fish, BD1-Water supply for drinking (with treatment) and growth and propagation of salmonid fish.

The existing treatment system was considered for modification on the basis that Silver Bow Creek would

By Jorge|2019-04-15T17:33:44-04:00April 15th, 2019|Categories: Environment & Tailings|Tags: 972|Comments Off

Continuous Mechanical Froth Flotation Cell

The BSA and DRC models have been shown to offer excellent alternatives to the NDRC model, given previously in the literature (1) in predicting the dynamics of glass bead flotation. Since the TP model converged to unrealistic parameter values and gave the poorest data fit, the TP model is judged unacceptable for predicting continuous mechanical, flotation cell dynamics, at least for this system under these test conditions.

Although the DRC model did not fit the data quite as well as the BSA model, this experiment should not be judged the best test of the model, since the glass beads were all of very nearly identical size and shape and must have had quite similar flotation properties. Thus only a small variation in floatability between particles was expected. In practice the floatable mineral particles would have a much wider range of floatabilities, and the DRC model should have much greater ability with such systems.

Essentially perfect mixing of liquid phase was shown to exist in this cell. The solid phase was slightly less well mixed, but the mixing was good enough for models based on perfect mixing to apply. It has been demonstrated, however, that perfect mixing in the liquid phase does not

By Jorge|2019-04-15T18:29:28-04:00April 15th, 2019|Categories: Flotation|Tags: 972|Comments Off

Consulting Geologist

One possible reason why some companies lack the wisdom to hire geologists is that they are dominated by engineers who still subscribe to the old idea that engineers are self-sufficient in all fields. They could have learned this from their professors, I once knew a Dean of Engineering who got purple in the face when a faculty committee was discussing the financing of a broad gauged engineering project and suggestions were made that assistance be obtained from the Schools of Business and Law and from some of the science departments. He pounded the table and shouted “Engineers are trained to handle all this.”

In addition to commodity knowledge a company may employ an outside consultant because of his prior field work in an area where the geology is strange to members of the geology staff. If the area is in a foreign country, a consultant with experience in that country could be a big help. He not only may know something about the local geology, but he also can help with previously acquired knowledge of how to obtain exploration concessions, the legal statue of aliens, the names and locations of pertinent bureaus, surveys, and other government agencies, the names and addresses

By Jorge|2019-04-15T18:27:14-04:00April 15th, 2019|Categories: Geology|Tags: 972|Comments Off

Coarse Grinding in a Ball Mill

Rod mills were developed as a logical substitute for the rolls crusher when larger tonnages had to be handled, on a continuous basis. Today, with even larger tonnages to process, the trend is to install larger equipment, automate the plant and develop the highest availability possible, in order to cut costs. The rod mills, because of design limitations in size and speed, are not able to meet these new requirements.

Practical Considerations

One of the primary reasons for investigating alternate flowsheets is the desire to reduce cost. Two flowsheets have been developed to compare capital and operating costs for a taconite plant with 4.5 million long tons per year concentrate production capacity at an assumed concentration ratio of 3:1.

The first flowsheet is a conventional circuit in which -¾” tertiary crusher product is fed to a rod mill drawing 4.6 Kwhr/Ton and producing an 80% -10 mesh product. At this stage 40% of the rod mill product is rejected in cobber magnetic separators as tailings. The cobber concentrate is ground in two ball mills in closed circuit with rougher, magnetic separators and cyclones. The calculated.ball mill power consumption is 13.8 Kwhr/Ton of crude. The cyclone overflow is deslimed, and upgraded in

By Jorge|2019-04-15T18:26:37-04:00April 15th, 2019|Categories: Grinding|Tags: 972|Comments Off

Biological Leaching Tests Dumps – Construction & Operation

Many papers have been published on the role of the bacterium Thiobacillus ferrooxidans in the oxidation of reduced sulfur compounds, and years of research have established the following environmental factors, which influence biological oxidation.

Construction

At the mine site, a 300 ft long, 60 ft wide road cut through a 50 ft high hill was selected for the construction of three test dumps. The road base, which had a 5% slope, was divided into three individual leaching areas by means of two 6 ft high, 12 ft wide, clay packed dams, which were sunk one ft into the road bed. The two outside dumps, which were the experimental dumps, were equipped with 4 inch diameter asbestos air pipes, spaced on 18 ft centers which were supported on a bed of 12 to 14 inches of crushed waste ore and covered with a 4 – 5 ft layer of the same material.

The area between the air pipes was filled with crushed waste in order to protect the pipes from the pit run waste ore which was to be dumped from the top of the hill side. The section of air pipe under the dump was perforated every 2 ft with ½

By Jorge|2019-04-15T18:26:03-04:00April 13th, 2019|Categories: Hydrometallurgy|Tags: 972|Comments Off

Basic Control Strategy for Mineral Processing

The principle purpose of applying control to any process is to improve its profitability. Even when considering the impact of a plant on its surrounding ecology this is still true, since the sanctions felt most immediately from violations of the regulations are the economic penalties or fines which result. Economic performance can be improved within a plant in several ways.

Control Techniques

The basic control techniques, of which examples from within the minerals processes will be given, may be itemized as follows:

i. Single loop feedback control
ii. Cascade control
iii. Feed forward control usually combined with one of the above
iv. Variable gain control
v. Predictive combined with adaptive control
vi. Optimizing procedures

The two most common difficulties which control loops have to be designed to cope with are process capacitance lags and transport lags. The first are introduced by vessel sizes and the delays in response occasioned by mixing phenomena. The control of density in a sump is subject to this last type of lag. Transport lags are exhibited when material has to travel a certain distance between a disturbance and the point where the response is measured. Both mixing and transport lags occur within the mill in a grinding circuit while a spiral classifier

By Jorge|2019-04-15T09:03:01-04:00April 12th, 2019|Categories: Grinding|Tags: 972|Comments Off

Bacteria & Hydrogeochemical Prospecting

Action of certain strains of bacteria has been implicated as a significant factor in the oxidation of ore deposits. Other bacteria are thought to be significant in the formation of syngenetic sedimentary ores and in supergene enrichment processes.

A normal soil/ground-water regime provides all of the necessary pH and Eh conditions for several groups of bacteria which influence the sulfur cycle in nature. Limiting concentrations of nutrients such as sulfate ions can determine whether a particular microbial species is active at a given place.

Sulfide producing bacteria (presumably sulfate users) were found in water from about 50% of wells sampled in the mineralized area and in about 30% of samples from the barren area. These bacteria ore readily detected and may provide a useful tool for regional geochemical reconnaissance. Bacterially produced sulfide ions can remove metals such as copper and zinc from solution thus complicating the interpretation of hydrogeochemical prospecting.

In our everyday experience we think of living forms (other than photosynthetic) as oxidising organic materials such as searches or proteins to produce primarily CO2 plus H2O and the energy necessary to get the creature about its daily tasks. Typically the energy available in this type of metabolism is substantial. Many possible reactions

By Jorge|2019-04-15T09:00:42-04:00April 12th, 2019|Categories: Mineralogy|Tags: 972|Comments Off

Advantage of a Crowd for Acid Waste Liquors

Because of increased pressure from Federal & State Regulatory-Agencies, most acid flows will require some sort of treatment prior to being discharged to receiving streams. In many industries, the volumes of liquors are large and their acid content varied.

“Standard” methods of acid neutralization with lime have been known for years, however, the volume and characteristics of the resultant precipitated solids can create a disposal problem. Also, when standard lime treatment is used, the settling characteristic of the precipitated solids is normally slow. In some instances, the necessity of added dissolved solids removal, (such as iron, needing aeration) add to the problem of concentrating neutralized solids.

The treatment consists of neutralization with a milk of lime solution followed by aeration to convert precipitated ferrous hydroxide to the ferric state, to reduce iron solubility, followed by sedimentation.

Clarifier overflow goes directly to a receiving stream. A percentage of settled solids from the clarifier are recycled to a lime reactor ahead of the neutralization tank. The remaining settled solids are pumped underground into an abandoned mine area.

This plant required a single 25-HP surface aerator, reaction tanks (with mixers), an 80′ diameter clarifier and a lime feeding system. Present lime usage is approximately 4 to 5 TPD