973

Miller Number – Slurry Rating Index

The development of a new means of measuring the relative abrasivity of a slurry came about by necessity in 1967 during a full scale loop test of a 560 H.P. reciprocating pump handling magnetite slurry. In order to evaluate the life of expendable fluid end parts, the question of the amount of attrition in a re-circulated slurry had to be considered.

Test Equipment

The device used to measure the relative abrasivity of various slurries consists in general of a standard ½” x 1″ metal wear block, driven at a rate of 48 strokes per minute, with a 200 mm stroke, riding in the bottom of a tray containing a 50% by weight slurry of the solids mixed in water. (Some tests are run in actual wet slurries as supplied.) A dead weight of five pounds is applied.

Standard procedures were adopted and a series of tests on available slurries and “pure” minerals were made. The test data was examined and it was noted that the abrasivity, or loss of metal wear block, was not the same for each incremental run, indicating a change of characteristics of the solid particles – apparently a “breaking down” due to the friability of the material.

How to Remove Mercury from Copper Concentrate

The copper-silver-mercury orebody of Gortdrum Mines (Ireland) Limited is located 3 miles north of the town of Tipperary in the Republic of Ireland.

The first shipments of concentrates were made to the smelter in Europe in late 1967. In the spring of the following year, word was received from the smelter that these early shipments contained between 1% and 2% Hg, and that the smelter could not accept further shipments of this quality.

Roasting was the only feasible method found for removing the mercury from the concentrate, and it was decided that this should be done in an atmosphere with limited oxygen.

Early Work

One of the first requirements was to establish the extent of the problem. An initial difficulty was with analyses. It was obviously desirable to know how much mercury was in the ore, and, since arsenic and antimony were important penalty elements in the copper concentrate, it was also important to be able to analyse the ore for these elements.

Reasonably reliable techniques were soon developed for the analysis of concentrates, although doubts about the absolute accuracy persisted for a considerable time. The methods adopted were atomic absorption techniques for mercury and antimony, and a distillation technique for arsenic.

 

Low-speed Gearless Converter Drive

The first motors of this type were built to drive ball mills in the cement industry, which are very similar to those employed for ore processing. Here, too, the tendency is to build units of ever increasing capacity. In the case of conventional drives with mechanical gearing, this involves correspondingly increasing difficulties.

Technical principle

A high-voltage supply is taken to a special type of transformer with three secondary three-phase systems. This transformer may be replaced by three separate three-phase units..The phase-angle-controlled converter cuts out one phase of the low-frequency three-phase supply from each of the three three-phase currents available from the transformer secondary. This frequency can be varied between 0 and about 50% of the system frequency, the latter value being the maximum for which the cyclo-converter can be designed. The low-frequency output of the converter is supplied to the stator circuit of a synchronous motor through special circuit-breakers. The thyristor gate control is activated by a digital speed transmitter, which ensures that the motor and converter are always in synchronism, i.e. the motor is safely prevented from falling out of step. The motor field circuit is supplied by a separate transformer with a controlled rectifier in the secondary circuit.

Hydraulic Excavator

First, the hydraulic excavator enjoys tooth forces of the shovel because the dipper is attached to the machine with a dipperstick and boom, and can often actually realize greater tooth forces than a shovel because of the prize action of the dipper in hard digging.

Digging range can be as deep as 35′ while dumping range in a 360°circle, can be as high as 26′ and this dump range circle can have a radius of 47′ with the current production machine. There are a variety of machine sizes. Generally speaking, the larger bucket machines have greater reach and digging depth. Also the larger mining type hydraulic machines can have special shorter range booms with correspondingly larger dippers. A new bigger machine with more than 60ft. of reach and 40 ft. digging depth is now at work in Wisconsin.

All excavators have a duty cycle rating. This is not lift capacity, rather it is a complex judgment by the manufacturer of considerations that allow the largest load of material or widest dipper for digging, considering tooth force for penetration, that the machine can reasonably live with for long economic and reliable service life. The duty cycle rating must take into consideration the dipper

Gypsum Calcining

Gypsum is the crystalline chemical compound CaSO4·2H2O. A close chemical relation – and frequently occurring with Gypsum – is Anhydrite which is CaSO4. Gypsun has wide commercial use because relatively simple heat processing reduces it to Plaster of Paris. While Anhydrite can be converted to Gypsum and thence to Plaster of Paris, the procedure is not simple and is quite costly. Anhydrite, however does have use in the agricultural field and in the Portland Cement industry.

The chemical compound of Gypsum, CaSO4·2H2O, breaks down into the following:

Lime (CaO)………………………………………………………….32.6%
Sulfur Trioxide (SO3)…………………………………………….46.5
Water…………………………………………………………………..20.9
Total………………………………………………………………….100.0%

Calcination of Gypsum was an accidental discovery as were its rehydration characteristics. Ancient man probably used lumps of Gypsum to enclose his fire. Some degree of calcination and softening occurred and when the fire was extinguished with water he noticed the lumps soon hardened. The next step was to break the massive Gypsum into small pieces and then to pulverize them in a hollowed out block of Gypsum or perhaps harder stone. The pulverized Gypsum was calcined in a vessel of some type, likely ceramic. The resulting product, eventually many hundred of years later, named Plaster of Paris, provided this early man with a medium for making cast objects.

In the

Grinding and Concentration of Conglomerate Copper Ore

The conglomerate ore analyzed approximately 1.2% copper. The specific gravity of the ore was 2.72 and the bulk density was 108 pounds per cubic foot (determined on “as is” ore). The Bond laboratory ball mill work index was determined as 22.0 at 65 mesh.

Autogenous Grinding Tests

Crude ore was fed manually to the mill, wet ground, and discharged through slotted grates and five pebble slots near the periphery of the grate. The pebble slots had approximately 2½-inch openings. A trommel on the mill trunnion equipped with a 3/16-inch screen, separated the minus 2½-inch discharge product into two size fractions. Trommel oversize was then screened to make 2 ½ by 1-inch and 1 by 3/16-inch fractions. Liberated copper in the 2½ by 1-inch product was removed by handpicking.

Liberated native copper was removed from the 1 by 3/16-inch fraction by jigging, and the jig tailings were returned to the mill. Minus 3/16-inch material from the trommel was also jigged to remove liberated copper.

Although no attempt was made to optimize the flotation circuit, 87.5% of the copper was recovered in a 46.9% Cu total concentrate during test A and 87.7% of the copper was recovered in a 60.5% Cu total concentrate during

Mining Project Financing

It scarcely is possible to read a new issue of any of the principal mining trade journals without noting some mention of a major new overseas mining venture with which one or more domestic companies are involved. These projects seem to follow a fairly consistent pattern; most are large open pit mines, with relatively low grade ore bodies but huge reserves; the total price tag will be in nine significant figures and around half or more of the total cost will be for infrastructure. West noted that nearly $7 billion is being invested annually for new mining projects and the expansion of existing mining ventures, in the free world.

Project Financing

Prior to the “carveout boom” of the 1960’s most of the major mining companies relied principally upon internally generated capital, plus occasional sales of equity, to finance new projects. Bank financing, to the extent that it occurred at all, was principally in the form of unsecured lines of credit for seasonal needs, largely for the use of manufacturing and fabricating subsidiaries. The rapid growth of conventional carved-out production payment transactions, which occurred during the last half of the 60’s decade, helped to stimulate other kinds of specialized financing by

Simulation of Dry Ball Milling using Specific Power

The energy-size reduction relationship was the dominant form of mathematical model used in the description of tumbling mill grinding processes. Typically, in these models some single measure of product fineness (e.g. the 80% passing size, the size modules, the specific surface area) is chosen as the dependent variable and the energy input per unit mass of material being ground acts as the independent variable. In some instances these models have been useful for the correlation of experimental data, but, invariably, they have been found to be inadequate for meaningful process simulation.

Experimental Data

The data examined here is a composite of data collected in two separate studies designed to evaluate the influence of various mill operating variables on the kinetics of dry batch ball milling. In each of these studies the feed material was 7 x 9 mesh dolomite prepared by nipping large single crystals in a roll crusher. Since there were small differences in the fragmentation characteristics of the two batches of feed used in these studies the two data sets associated with these feeds will be distinguished by referring to them as BATCH 1 data and BATCH 2 data in the text.

The range of mill operating conditions considered

How to Control Briquet Quality

The application of briquetting in various chemical, mineral, mining and metallurgical processes has been rapidly increasing in the past two decades. This is, in part, due to the development of new, more economical and higher performance briquetting equipment. Some of these developments, which have reduced the operating and maintenance costs, include anti-friction bearings, hydraulically applied pressure enclosed and sealed gearing and bearings, tapered predensification feed screws, water cooling and materials of construction capable of operating at temperatures up to 1800°F, and control systems capable of maintaining optimum briquette quality control.

The briquets can be formed into almost any desired size and shape. To date, with present rotary briquetting presses in the 25 to 500 ton force range, briquets from ¼” to 6″ length are presently being used. The screw force feeder, which can be of various taper configurations or straight, performs several other functions in addition to feeding the material to the press rolls. Of equal and possibly greater importance, they (1) predensify or precompact the material, prior to its entry into the roll forming dies, (2) apply a precompaction pressure to the feed material and (3) deaerate the feed material by means of the precompaction pressure. These functions have a

Continuous Particle Size Analyzer for Metallurgical Slurries

A continuous on-line particle size analysis system for solid/liquid suspensions is described. The basic sensor utilizes a centrifugal principle to separate particles according to size, the resultant separation being measured by means of beta-ray attenuation. Results obtained when analyzing a variety of materials at sizes from 65 mesh (210 microns) to 20 microns are discussed in detail. Accuracies better than 2% are demonstrated.

Sampling and Slurry Handling

A suitable sampling device for the abstraction of a small continuous, representative sample from a closed pipeline has been described in an earlier paper. The instrument detailed in this article requires a constant sample flowrate at a reasonably constant solids content. The flowrate required depends upon the size at which a measurement is required. The importance of this will be discussed later. The flowrate required for a measurement at 150 mesh (105 microns) is. 2.2 GPM (flow velocity 13.9 ft/sec), and this is achieved by means of a head tank system. The slurry stream from the sampler passes through a 16 mesh screen, designed to remove tramp oversize. Dilution water, controlled by means of a density signal from the analyzer, also is added via the screen. The diluted slurry passes to a small baffled

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