1977-78

How Maintenance Practice Affects Wire Rope Life in Surface Coal Mining Draglines

As part of a larger study to identify factors influencing the practical operating life of wire rope used on large draglines in surface coal mining, field trips to operating surface coal mines were made during late 1975. Wire rope performance information was obtained from personnel at thirteen mine sites west of the Appalachians.

Data Acquisition

During the field visits, mine operators provided rope life information about their machines. Some of the rope life data consisted of gross averages; other data was in the form of detailed records, including rope construction and manufacturer, cutoff and resocketing periods, end-for-end switching, and downtime for rope change-out.

Some form of data normalizing, however, was considered desirable. One apparently useful factor was the amount of cross-sectional wire performing the hoist or the drag function. A simple expedient was to sum the squares of the nominal rope diameters used in each function and divide that number into the total yards handled until retirement. The performance of draglines with different bucket sizes could then be crudely compared, since the normalizing factor is approximately proportional to the actual cross-sectional area of the wires in the rope (and hence the weight per unit length of rope, or, roughly, the cost

By |2019-02-07T13:20:03-04:00January 31st, 2019|Categories: Mechanical & Maintenance|Tags: |Comments Off on How Maintenance Practice Affects Wire Rope Life in Surface Coal Mining Draglines

Control Wet Grinding Circuits

Ideally, mill circuits should be controlled so that excessive random disturbances are reduced in frequency and amplitude. It is difficult to derive an objective measure of the effectiveness of any chosen control strategy. Often, the response of the circuit to pulse or sinusoidal disturbances is used as a measure of the effectiveness of control.

Linear Mill Models and Stochastic Control Theory

One approach to the problem of modelling dynamic systems subjected to random process disturbances is to postulate a priori that the system can be modeled by a finite set of linear, time invariant stochastic differential equations of the form

wet-milling-circuits-equation

where Xt is the state variable vector and Wt is a vector of Wiener processes which form the basis for modelling process disturbances. A is the system matrix and D is a matrix of disturbance influences. Measurable outputs of the system described by Eq. 1 can be expressed as a linear function of the state variables

wet-milling-circuits-equation-2

where Yt is the output vector and C is a constant matrix. The controller proportional bands and integral reset times will be imbedded in the elements of the matrix A. The

By |2019-02-07T13:19:07-04:00January 31st, 2019|Categories: Grinding|Tags: |Comments Off on Control Wet Grinding Circuits

Wet Dielectric Separation

It was studied the possibility to use electrical phenomena in order to selectively separate minerals with various densities and dielectric constants in non-homogeneous electric fields. This technique is based on levitation forces acting on a solid particle immersed in dielectric fluid.

When the gradient of the electric field is directed downwards, the levitation force in the dielectric fluid (pure liquid or electric colloids) will be in an upward direction to float sinking minerals by counterbalancing their density mismatch with the liquid medium.

Pondermotive Forces

A dielectric fluid characterized by its dielectric constants εm and its electrical resistivity pm. The problem is to evaluate the force acting on a solid particle (dielectric constant ε1, resistivity p1) immersed in the liquid, in which a field E(x) exists which depends on the position.

When a particle (that we shall suppose to be spherical) is placed inside the dielectric medium, it may be acted upon by three forces:

If the particle is charged, there is a force proportional to the field, F = VQE (where V is the volume of the particle and Q its charge density). In the following we shall suppose that the particles are neutral and thus we do not consider further this force.
If

By |2019-02-07T13:18:21-04:00January 31st, 2019|Categories: Magnetic|Tags: |Comments Off on Wet Dielectric Separation

Vacuum Filtration

In reviewing available vacuum filtration equipment in this paper, several types of filters have been included which are probably not familiar to operators in the mining industry. However, it was felt that these units might be of interest in the event that an application should arise for the filtration of a product in the future that does not exist today. In addition, exposure of our industry to equipment used in other industries might have a tendency to be thought provoking and perhaps lead to the development of equipment and/or applications in our industry which do not necessarily exist at this time.

Fundamentals of Vacuum Filtration

Filtration may be defined as the separation of solids from a liquid effected by passing the liquids through a porous medium. If the filtrate is induced to flow through the medium by hydrostatic head, we refer to it as gravity filtration. If we utilize super-atmospheric pressure upstream of the medium we call it pressure filtration and if sub-atmospheric pressure is applied downstream of the medium we call it vacuum filtration. Centrifugal filtration occurs when a centrifugal force is applied across the medium. Centrifuges will not be discussed in this paper.

The process goal of filtration may

By |2019-02-07T13:25:10-04:00January 30th, 2019|Categories: Filtering|Tags: |Comments Off on Vacuum Filtration

Uranium In Situ Leaching its Advantages – Computer Simulation

In Situ leaching for the recovery of uranium from low grade sandstone deposits is one of the newest technological advances in the mineral industry. It is rapidly developing into a commercially feasible mining system which has economic, environmental, and social advantages over conventional mining systems. Because of the current uranium shortage, development of In Situ leaching into a sophisticated system has gained new impetus. In Situ leaching will become an important mining technique in the future, which will greatly help to supply uranium for our nation’s energy needs.

Environmental Overview

From the environmental standpoint, solution mining of uranium shows a negligible effect on such factors as surface disturbance, interference with natural groundwater quality and distribution, and aerial discharge of radionuclides. In the surface disturbance category, only one to two pounds of tailings per pound of uranium result in acid leaching and virtually none in the carbonate leaching system, which compares very favorably to the half ton of waste produced per pound of Uranium produced from conventional systems. Additionally, the only other surface disturbance is that of clearing the area of brush and trees and grading roads to the area.

State-Of-The-Art

Solution mining requires some specific geological conditions to allow recovery

By |2019-02-07T13:24:33-04:00January 30th, 2019|Categories: Hydrometallurgy|Tags: |Comments Off on Uranium In Situ Leaching its Advantages – Computer Simulation

Solvent Extraction Economics

The equipment which is used in solvent extraction plants for contacting the organic and aqueous phases and separating the same is varied. Most common to the industry is the mixer-settler unit which, in itself, can be of varied design; but many new innovations in contacting and separating equipment have been recently introduced or are now being studied.

Reagents

Each solvent extraction reagent must possess a number of properties or criteria before it can be economically used in a process to recover a given product. The value of the product will often dictate the degree to which a reagent must meet these criteria.

Listed below are some of the more important properties, according to Swanson and the possible impact each may have on the economics of a solvent extraction process:

  1. Capable of selectively extracting some ion or ions under specific conditions; excellent selectivity can result in the elimination of extraction or wash stages and can reduce expensive bleed streams,
  2. Kinetically fast in reaction; fast reactions result in smaller mixing equipment, thus a smaller reagent inventory and sometimes a lower mixing power equipment,
  3. Capable of reacting, reversibly; the reagent must be stripped or regenerated under conditions that allow the final product to be
By |2019-01-30T05:12:46-04:00January 29th, 2019|Categories: Hydrometallurgy|Tags: |Comments Off on Solvent Extraction Economics

Sulphidized Cassiterite & Iron Oxides Separation

Low recoveries of cassiterite are obtained by gravity concentration of lode deposits, particularly if the cassiterite calls for fine grinding of the ore. And it is precisely this finely ground ore that is the cause of the low recoveries.

The possibility therefore of upgrading the ore by flotation has been of great interest to the tin industry because flotation, in general, produces high recoveries from other finely-ground metal ores. Many attempts have been made to float cassiterite directly. This paper is a summary of our work on sulphidization of cassiterite, iron oxides, the dissociation of pyrite and their subsequent flotation and separation, in artificial mixtures and natural ores.

Investigation Plan

While there were many steps in our investigation plan, the major phases of our investigation were:

  1. Microscopic analysis of the products of cassiterite sulphidization, with the variables: (a) particle size, (b) time for sulphidization (c) temperature during sulphidization;
  2. Sulphidization Flotation tests using high-grade cassiterite; testing the following variables: a) Particle Size; b) Temperature of Sulphidization; c) Time for Sulfidization.
  3. Sulphidization – Magnetic Separation-Flotation of: a) high grade hematite ore and b) magnetite ore.
  4. Thermal dissociation of pyrite, testing the following variables; a) Size fraction; b) Time of dissociation; c) Temperature.
  5. Flotation and
By |2019-01-28T14:54:53-04:00January 28th, 2019|Categories: Flotation|Tags: |Comments Off on Sulphidized Cassiterite & Iron Oxides Separation

Semi-Autogenous Grinding of Copper Ores

Mechanism of Size Reduction

The spectrum of comminution mechanisms in a mill range from shattering of the rock by imposition of a load to abrasion by surface contact with other rocks. Since SAG represents a combination of autogenous and ball milling, a better understanding of the mechanism of the comminution process in a SAG mill can be obtained by examining first the information available on autogenous grinding.

In an interesting study of autogenous grinding in a 10-ft. dia. x 2-ft. long Cascade mill:

semi-autogenous-grinding-equation

where Do: diameter of new balls to the mill

In more general terms, the Gaudin formula for comminuted particles expresses the % weight of particles reduced to size D1 as being proportional to

semi-autogenous-grinding-equation-2

Where D0 represents a size modulus representing the initial size of the particles, and “n” corresponds to the inclination ∝ (n = tan ∝) of the cumulative particle size distribution in the mill after comminution (plotted on a log-log scale).

The pilot tests in the 10-ft. mill showed that when the autogenous mill was fed with a narrow fraction of particle sizes, ranging from 150-mm. to 40-mm, after comminution the inclination factor n ranged

By |2019-01-28T14:55:37-04:00January 28th, 2019|Categories: Grinding|Tags: |Comments Off on Semi-Autogenous Grinding of Copper Ores

Selection and Combustion of Pulverized Coal in Rotary Lime Kilns

The selection of a coal for direct pulverized firing of a rotary lime kiln may be determined by trial and error, persistence of sales personnel, proximate analyses, grindability, or apparent BTU cost. Occasionally, the only question asked is, “How much lime will it make?”

The classic three T’s – time, temperature, turbulence – must be enlarged upon for a better understanding of the problem. Pulverized coal occupies only 0.01 per cent of the volume of air required for its combustion. This mixture behaves like a gas and the general laws governing the movement of solid particles in gasses are in effect.

As combustion proceeds, the weight of solid remaining becomes less, keeping the particle bouyed up longer in the gas stream. As the distance from the burner tip increases, turbulence decreases. Eventually, the particle of carbon or coke reaches its terminal velocity in the gas stream. This is a most unfortunate situation. The volatiles which burn readily are available for ignition at the point of highest turbulence in the coal-air stream and the carbon residues which burn more slowly only become available for combustion in the very low turbulence and low oxygen portion of the flame. The combustion rate of the solid

By |2019-01-28T14:55:52-04:00January 26th, 2019|Categories: Pyrometallurgy|Tags: |Comments Off on Selection and Combustion of Pulverized Coal in Rotary Lime Kilns

Partially Saturated Zone Beneath Tailings Impoundments Seepage

Conventional analyses of seepage through saturated media do not apply when tailings impoundments are located above a partially saturated zone. Three stages of seepage are identified and methods for estimating the seepage rates and duration of each stage, based upon flow in partially saturated and saturated porous media, are demonstrated. The effectiveness of earthen liners is discussed and procedures for estimating the required properties of the porous media, are provided.

Summary of Methods of Analysis

The idealized profile of the tailings and foundation material and the phreatic surfaces in the impoundment and underlying aquifer are studied. Seepage from beneath the impoundment is conveniently viewed as taking place in three distinct stages designated as Stages I, II, and III. These stages are considered separately and are defined as follows.

Stage I. – During this stage a wetting front advances downward through the partially saturated underlying foundation material. Above the wetting front, the material may or may not be saturated.

Stage II. – When the wetting front contacts either an impervious stratum or the phreatic surface of an aquifer, a ground-water mound will develop and rise toward the impoundment. Stage II, represents the time interval during which the mound is developing.

Stage III. – After the

By |2019-01-28T14:56:26-04:00January 26th, 2019|Categories: Environment & Tailings|Tags: |Comments Off on Partially Saturated Zone Beneath Tailings Impoundments Seepage

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