Recovery Of Magnetite Research Articles

Recovery of pyrrhotite and magnetite from tailings of Norilsk disseminated sulfide ores

Recovery of pyrrhotite and magnetite from tailings of Norilsk disseminated sulfide ores

The development of a magnetic hydrocyclone for processing finely-ground magnetite

Previous models of magnetic hydrocyclones were successful in improving the separation of magnetically-susceptible particles from a carrying liquid. Problems occurred, however, with magnetic particles flocculating and accumulating within the hydrocyclone. The liquid flow patterns in the hydrocyclone became distorted, leading to a dilute solid product. A new design of magnetic hydrocyclone has been developed using Nd-Fe-B magnets, which overcomes the problems of magnetic accumulation. The magnets are used to pre-direct the hydrocyclone feed. Compared with a conventional hydrocyclone, this magnetic hydrocyclone is approximately 13% more efficient in the recovery of magnetite, with no change to the liquid content of the product. In an appropriate industrial application, the use of this type of magnetic hydrocyclone could produce significant reductions in the size of installation and processing time. >

An integrated heavy media cyclone-flotation system for coal cleaning

Flotation was used to achieve improved separation of magnetite from the float and sink products obtained from heavy medium separation and to reduce the load of the medium cleaning circuit. The investigation was carried out in two successive phases. In the first phase, tests were performed on in-plant samples from the Homer City Coal Prepation plant to determine what effects variables such as medium density, particle size and magnetite source had on the efficiency of the process. In the second phase, the optimum conditions determined in the first phase were used to determine the applicability of the process to other selected coals from central Pennsylvania. It was observed that flotation was very effective in the separation of magnetite from coal. In most of the cases investigated, the magnetite recovery was approximately 99% with a magnetite grade ranging from 95 to 99%. The grade of the magnetite decreased as the ash content of the coal increased and the particle size of the magnetite decreased.

Magnetite Heavy Media: Standards and Testing Procedures

Magnetite heavy media processes are accurate, efficient and easy to control separators, capable of producing high quality clean coal. Magnetite recovery circuit operation and magnetite consumption are the main reasons for high capital and operating costs. Over the last two decades, several countries have been actively involved in establishing magnetite specifications for coal heavy media circuits and in developing working standards for test magnetite. This paper reviews media recovery circuits, operating parameters for magnetic separators, magnetite consumption and specifications for heavy medium magnetite. It discusses methods and instruments used in the determination of those physical and chemical properties of magnetite, and rheological properties of magnetite suspensions which are relevant to the application of heavy media separators. The paper also outlines the development of the international standards for magnetite and magnetite suspensions testing.

The Design and Operation of Heavy Medium Recovery Circuits for Improved Medium Recovery

Abstract In dense medium processes for the beneficiation of minerals the consumption of medium (generally ferrosilicon) represents a major component of the operating cost. This provides a strong incentive for improvement in heavy medium recovery circuit design and operation. A major thrust in heavy medium plant design over the past decade has therefore been towards circuits which reduce medium losses. In this paper recent trends in plant design are examined in relation to the factors influencing circuit performance and medium losses. Operational details which have a significant effect on losses are discussed and illustrated by means of plant and pilot plant test data, with particular emphasis on the performance of wet drum magnetic separators. While the emphasis is on reducing the consumption of the high-cost ferrosilicon medium used in minerals beneficiation, most of the principles described in this paper are equally relevant to the design and operation of magnetite recovery circuits for coal preparation...

Moisture of air and efficiency of dry magnetic separation

The authors mathematically formulate the efficiency of a magnetic separator for the recovery of magnetite and quartz and assess the effect of atmospheric humidity and consequent ore moisture on losses in efficiency in the separator. They propose a preliminary drying treatment and justify the expenditure of energy this requires by demonstrating that the overall efficiency of the drying and the consequent moisture-free separation process exceeds the efficiency of the separator when moisture is allowed to remain a factor in the process.

Continuous heavy medium recovery by high gradient magnetic separation (HGMS)

Fine magnetite in water, used as a heavy medium for cleaning fine coal in cyclones is recovered for recycling by magnetic separation. HGMS has been introduced to this application of magnetic separators to improve magnetite recovery, increase material throughput rates and reduce plant space and flow sheet complexity. A continuous separator would be required when the feed slurry is dense and when matrix loading occurs quickly. Following laboratory batch separations, a test program was conducted on a 1.85 m diameter carousel continuous separator. The results were in close correspondence to the earlier batch work demonstrating that high magnetite recoveries are possible at high flow rates along with minimal coal retention in the magnetics.

Critical pressure drop and flow velocity in axial HGMS matrices

The material throughput per unit area, v, is an important parameter for magnetic separation. Another is the pressure drop (as head loss due to flow per unit length of matrix, P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</inf> . The value of v for which P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</inf> = 1 is designated v <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> which depends on the characteristics of the slurry and on matrix construction but not on matrix length or area. In the absence of magnetic field, data can be matched to a curve of the form: <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p_{n} = (\frac {v}{v_{c}})^{2}</tex> for relatively open matrices and high velocity. When slurry "pours" through a matrix, as in the present experiment, with no velocity control, the flow tends to satisfy a condition of balance between head and head loss corresponding to P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</inf> = 1. In a magnetic field there is a value of P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</inf> , P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> , which controls the trapping of magnetics. Experiments indicate that magnetics trapping of efficiency is high only for P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</inf> < P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> . Three screen spacings were used in batch experiments on the recovery of magnetite from magnetite/coal slurries from coal cleaning plants. Two of these have been transferred to continuous carousel separator matrices. Pressure drop as a function of velocity was measured on the batch matrices to help in the design and in the operation of continuous tests.

Magnetite-coal separation by continuous HGMS

Magnetite, slurried in water, is used to create an apparent heavy medium in which fine coal (0.1 to 2.4 mm) is cleaned of its mineral impurities. The magnetite is much finer in size (1 to 44 μm) than the coal and is usually recovered from the coal and refuse by magnetic drum separators. Their performance suffers from changes in feed conditions and a number of them are needed for the average coal cleaning plant. We have adapted HGMS for magnetite recovery because of its insensitivity to coal/magnetite ratio and slurry density and its ability to capture fine magnetite at high velocity. An open vertical matrix able to capture 10 μm (avg. size) magnetite without entraining 2 mm coal has been incorporated in a 1.85 m diameter continuous separator. Three-quarter ton samples of magnetite (in 1000 gallons of water) have been recovered with the matrix ring turning at 40 cm/s through a field of 6 kOe. A laminated core demagnetizing coil followed by water sprays removes the recovered magnetite. In preparation for this continuous program, tests of slurry densities from 20 to 35% solids and coal/magnetite ratios'from 3:1 to 1:4 showed almost no variation in recovery or entrainment. A 4.8 m diameter separator, the largest currently available, with multiple heads, should be able to treat 350 tons of magnetite and coal per hour.

Improved magnetite recovery in coal cleaning by HGMS

A research program at this Laboratory has demonstrated successful recovery of magnetite at high throughput rates from mixtures of magnetite and coal-like those found in a coal-washing circuit-by High Gradient Magnetic Separation (HGMS). Improving the rate of magnetite recovery with HGMS over that found with conventional magnetic separators is an achievement important to the coal cleaning industry. A single-stage separator was used at rates up to 4.4 tons per hour per square foot of matrix cross-section. At this rate more than 99% of the magnetite was trapped along with less than 5% of the coal, an improvement over drum separators working in the particle size range of the feeds used in this study. Data is presented on the effect of loading on magnetite recovery and on non-magnetic material entrainment in the magnetic fraction. This fraction increases with increased loading indicating non-magnetics trapping but the effect is least at the highest material throughput values. Dispersants help to reduce entrainment, also. Some magnetic agglomeration appears to occur as the separation is performed but there seems to be little difference in separator performance on the basis of particle size.

Magnetic separation equipment for coal applications

This paper covers the use of magnetic separation equipment to remove "tramp iron" from processed coal to protect possible damage to belts, cruhers, hammermills, and screens. It also covers the use of "wet drum separators" in the recovery of magnetite from heavy media plants. Selection criteria are discussed.