New quarry screens for processing crushed rock rejects with high moisture content

In production of gravel from crushed rock, rejects with particles smaller than 5 mm form, which in most cases are not used and are considered a waste because they do not lend themselves to further "dry" fractionation by technical means available to enterprises. The waste is stored in dumps creating serious economic and environmental problems.

Processing the rejects on traditional screens presents difficulties both in current production and in screening the content of dumps. The former causes rapid blinding of fine sieves, the latter becomes impossible due to the high moisture content of the material, which causes sieve blinding already at a moisture content of 2-3%.

When igneous rock is crushed by cone crushers, the rejects account for more than 25%. Centrifugal crushers produce cubiform gravel, the demand for which is constantly growing, together with rejects whose content in the crushed gravel reaches 50%. On the average, the rejects of carbonate rocks in the industry make up 40% of the processed rock.

A small proportion of rejects is processed by "wet" method, which entails the need for large amounts of water and sewage treatment facilities for its clarification. Despite this, hundreds of millions of tons of materials extracted to the surface continue accumulating in the dumps due to the lack of "dry" methods of their processing. At the same time, modern industry is in dire need of technical means that can expand the range of high quality construction materials from the crushed rock rejects. Such materials can be used as a substitute for natural sand in road construction, production of concrete and asphalt mixtures, plaster, dry construction mixtures, granite chips for the manufacture of roofing, paving, water filters, small architectural forms, etc.

Kroosh Technologies Ltd has developed and manufactures multifrequency vibration machines, which solve the problem of "dry" screening of wet rejects on 5 to 0.5 mm sieves directly at quarries and stone crushing plants. As this takes place, the range of the obtained products is not limited to the sands separated from the rejects but also extends to the production of fine wet gravel with a particle size of 10 mm and below.

The distinctive design element of the screens is an original mechanical system, which converts single-frequency vibration of the body into multifrequency vibration of the screening surface with a wide range of frequencies and acceleration peaks of hundreds of g. The result is a continuous self-cleaning of screens, high specific capacity and product quality with a relatively small dimensions of the sieve and low energy consumption.

In general, the scope of efficient use of multifrequency screens for screening bulk materials can be determined from the table. The possibility of screening a specific material in a given range of sieve openings depends on its size, type, presence of impurities, moisture and its type (internal or external).

 

Material Moisture Content, %

Sieve Opening Size, mm

0-0,2

0,015-0,7

0,2-0,5

0,1-1,0

0,5-1,0

0,25-2,0

1,0-3,0

0,5-3,0

3,0 -6,0

1,5-5,0

6,0-10,0

4,0-12,0

 

To screen such materials at granite and limestone quarries and stone crushing plants, medium- and heavy-duty screens are used. Medium-duty screens are available in single-deck version and are designed for a capacity of up to 50 t/h depending on the size and shape of the sieve openings and the moisture content of the feedstock. Heavy-duty screens are available in single- and double-deck versions and are designed for a capacity of up to 130 t/h.

For "wet" screenings of the rejects, specialized equipment is offered, which includes multifrequency screens for wet screening of granular materials with supplementary irrigation and multi-unit installations for desliming slurries.