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THE SEPARATION OF MATERIALS USING SELECTIVE MAGNETIC COATING.

Objective

THE PROCESS, THAT HAS BEEN ALREADY APPLIED SINCE 1979 IN THE PLANT OF MANTOUDI (GREECE) FOR THE SEPARATION OF SERPENTINE AND MAGNESITE, IS VERY INTERESTING FOR A NUMBER OF ORES WHICH DO NOT RESPOND TO CONVENTIONAL METHODS OF TREATMENT.
THEREFORE, THE DEVELOPMENT OF THE PROCESS, DEPENDING MAINLY ON THE SELECTIVITY OF THE MAGNETIC COATING ON THE DIFFERENT MINERALS, COULD BE OF GREAT HELP TO PROCESS ENGINEERS IN MANY DIFFICULT PROBLEMS OF SEPARATION, AS, FOR EXAMPLE, SEPARATION DOLOMITE/CALCITE/APATITE, SLIME CASSITERITE/QUARTZ, CALCITE/SCHEELITE, PHOSPHATE WITH CARBONATE GANGUE, ETC.
Development of a selective magnetic coating process for the separation of mineral pulps has been undertaken. Effects of surface properties, and the use of reagents to control these parameters, were studied in depth. A variety of waste products were studied as alternatives to magnetite for adsorption on to the mineral surfaces. Also, mathematical models of the behaviour of magnetic separators have been developed.

The principal conclusions of the work were:
the surface adsorption density of magnetic coating formed is strongly dependent on the particle size of the coating material;
use of oils allows coarser coating materials to be used;
high coating levels occur when the forces of interaction between the target particle and the coating particle are attractive and when the forces of disruption are low;
a model for the recovery of magnetite coated particles by wet high intensity magnetic separation has been developed;
a model for magnetic wet drum separation for the recovery of magnetic flocs has been developed;
the magnetic coating process is applicable to coarse particle separation;
BOS slime, from steel production, is of particular interest for use in the coating process;
magnetic coating processes can be run successfully on a pilot scale using conventional mineral processing equipment.

The objective of the research was to develop the selective magnetic coating process to a stage where it could be implemented industrially. The aim was to achieve this through an understanding of the fundamental processes which lead to the selective adsorption of fine magnetite onto mineral surfaces in mixed pulps and to apply the findings at pilot scale.

Results from the research have shown that the surface adsorption density of magnetic coating formed was strongly dependent on the particle size of the coating material. Under mixing conditions typical of industrial mixers particle adhesion on smooth surfaces was only significant when the coating particles were below about 2 um.
The size of the target particle over the range of 20 to 1000 um did not have a big influence on the density of the coating (weight of magnetite per unit surface area). Also, high coating levels occurred when the forces of interaction between the target particle and coating particle were attractive (or when there was only a low energy barrier to overcome) and when the forces of disruption were low. Hydrophobic surfaces, low zeta potentials, high ionic strength, surface hydrocarbon chains and bridging flocculation tended to favour adhesive coating formation. When oil was used capillary forces became operative.

A model for the recovery of magnetite coated particles by wet high intensity magnetic separation has been developed. As was a model for magnetic wet drum separation for the recovery of magnetic flocs.

It was also found that the magnetic coating process was applicable to coarse particle separation and the performance of selective magnetic coating as applied to phosphate processing appears promising. Various commercially produced magnetites and also waste products have potential for use in the coating process and magnetic coating processes can be run successfully at pilot scale using conventional mineral processing equipment.
THIS PROJECT ON THE SEPARATION OF MINERALS USING SELECTIVE MAGNETIC COATING WILL BE COLLABORATIVE BETWEEN WARREN SPRING LABORATORY (WSL) AND BUREAU DE RECHERCHES GEOLOGIQUES ET MINIERES (BRGM). THE OVERALL AIM OF THE PROJECT WILL BE TO IDENTIFY CONTROLLING PARAMETERS FOR THE SELECTIVITY OF THE PROCESS AND TO INVESTIGATE PRACTICAL PROBLEMS RELATED TO THE SCALING UP AND THE EFFICIENT AND ECONOMIC RUNNING OF THE PROCESS IN COMMERCIAL OPERATIONS.

THE WSL COMPONENT WILL STUDY THE FUNDAMENTAL ASPECTS OF THE PROCESS BY INVESTIGATING THE INFLUENCE OF SURFACE CHEMICAL AND HYDRODYNAMIC PARAMETERS ON THE SELECTIVITY OF THE MAGNETIC COATING FORMATION.

THE BRGM COMPONENT WILL MAINLY COVER INDUSTRIAL APPLICATIONS AND PILOT PLANT TESTWORK IN THE TREATMENT OF PHOSPHATE ORES, TOGETHER WITH SOME FUNDAMENTAL WORK ON THE SURFACES OF SULPHIDE MINERALS.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Warren Spring Laboratory
Address
Gunnels Wood Road
SG1 2BX Stevenage
United Kingdom

Participants (1)

Bureau de Recherches Géologiques et Minières (BRGM)
France
Address
39-43 Quai André Citroën
75739 Paris