Multi-Force Dewatering for Magnetic Waste Materials


The ability to effectively dewater many industrial wastes is often a severe limitation in their recycling or disposal. Wastes from steel-making frequently fall into this category, and there are numerous steel plants, and allied industries, operating around the world producing large quantities of such waste. Many of the waste slurries from the steel industry are characterized by their low solids content (< 25% solids by weight), high iron content (> 50% Fe), high content of magnetic material (> 50% Fe3O4), and fine particle size (< 25 μm). These properties often preclude effective dewatering, which is necessary to reduce the volume of the waste materials for disposal or recycling. In addition, an effective dewatering process can produce a solids-free liquid product, which can be recycled or discarded as a non-hazardous stream. This paper deals with the development of a novel process for dewatering waste pulps containing fine, magnetic material. The process involves chemical flocculation in a magnetic field and the application of a vacuum to remove the water from the flocced pulp producing a filter cake and a filtrate. The patented technique of multi-force dewatering has been implemented through the construction of a novel piece of equipment, consisting of a vacuum drum filter fitted with an internal, fixed magnet. A rare earth magnet fabricated by Eriez Magnetics of Erie, PA, has been incorporated into a laboratory vacuum drum filter by WesTech Engineering Inc. of Salt Lake City, UT. The paper describes the results of multi-force dewatering tests using artificial magnetic mineral pulps and actual steel plant wastes. It has been shown that the application of a magnetic field significantly alters the filtration mechanism for pulps containing magnetic particles. The filter cake appears to be kept open, possibly due to the formation of channels resulting from the alignment of magnetic particles along the lines of magnetic force. This permits a thick filter cake to be formed while maintaining filtrate flow through the bed. The overall result of the multi-force filtering is a large increase in filtration capacity. © 1994.


Materials Science and Engineering

Keywords and Phrases

Filtration; flocculation; magnetic field; magnetic wastes

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Document Type

Article - Journal

Document Version


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Publication Date

01 Jan 1995