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Development of a new treatment process for wolframite slime tailings.

Objective

The overall aim is to develop a new slimes treatment process for Community wolframite deposits (France, Spain, UK, Portugal) giving the 2-fold benefit of enabling practical reprocessing of historic tailings and intensification of current benefication processes.
Feed preparation of the wolframite slime tailings to be treated has been shown to be fundamental. A 3 stage concentration process was shown to be the most desirable. Firstly, primary roughing: the best overall performance is obtained if a gravity concentration device is used for this stage. An MGS or centrifugal jig was shown to meet the technical requirements. Jig performance was shown to be enhanced if feed is preclassified. The use of magnetic separation for this stage could not be recommended for the Beralt material as lower wolfram recoveries can be expected while the 3% grade could not be met. Flotation proved to be undesirable.
Second stage roughing: by MGS, centrifugal jig or Duplex. The MGS was shown to give the highest upgrade ratio but it is doubtful whether a discardable tail could be achieved by any one machine.
Sulphide flotation after stage 1 or after stage 2 should also be included. The positioning of this sulphide flotation step should not greatly affect the overall technical performance. It is unlikely that high recoveries of either copper or zinc can be obtained unless sulphide flotation is positioned prior to the primary roughing stage. An estimated 40% to 65% of the copper and zinc may be lost in the primary roughing stage. These figures will be sensitive to the first stage operations.
Thirdly, cleaning: a gravity cleaner circuit should then produce a final concentrate grade of 50 to 58% wolframite (WO3). Attempts to produce concentrates above this grade resulted in a rapid drop off in recovery. Testwork has indicated that the Duplex will perform this duty satisfactorily. Further upgrading of final concentrate can be done through the implementation of additional process stages and these include low intensity magnetic separation to remove ferromagnetics and acid leaching using warm nitric acid to dissolve residual sulphides and carbonates.
It has been shown that one or more dewatering stages will be needed in the circuit, especially if centrifugal jigs are to be used.

Overall recoveries of 70% to 73% of the 125 um to 10 um wolframite should be attainable with a 3 stage gravity concentration circuit. Based on the indications that 70% to 75% of the total tungsten contained in the overall tailings would pass to the concentration circuit, overall tungsten recoveries of 50% to 56% are predicted for the bulk dam material.

The recovery of tungsten from historic slimes dams at Beralt has been shown to be technically and economically viable, the rate of return on capital investment, however, is dependent upon the tungsten market. The technology is also applicable to minerals of similar physical properties.
The project will culminate in a pilot plant demonstration of the new processes and computer simulation of the integrated operation. An economic evaluation will be made in the context of the EC strategic requirements for tungsten (community customers, import substitution, possible import quotas, etc).

The project will involve the following stages.

Sampling the Beralt old tailings lagoon to study geographical variability, chemical alteration and mineralogical study. Based on the initial sampling results specific areas of the tailings lagoon will be selected for further detailed testwork. Individual samples will be prepared in quantities between half a ton and one ton.

Material characterization involving: a mineralogical study in order to get information relevant to the exploitation of byproducts and the environmental implications; chemical analyses and X-ray fluorescence for the major components; particle size laser diffratometry analyses; and chemical analyses, density, magnetic susceptibility distribution between the different particle size fractions, separated by cycloning.

In the modelling and simulation stage, gravity and magnetic models, already developed for coarser materials, will be extended and validated to wolframite tailings. High resolution gravity and magnetic simulation models will be developed. Efficiency of separation will be particularly modelled. Feasibility studies will be used to design the experiments. Analysis of experimental results will be used to improve the models to establish flowsheet and calculate mass balance, flow rates and concentrations of all streams of the multistage processes developed.

Gravity testwork will use modern high efficiency slime separators (Mozley multi-g separator and GEC Duplex). Results will be compared to standard shaking tables efficiency. Special studies willbe made on: frequency and amplitude of vibrations; machine settings (slope, g force); and feed characteristics (rate, liquid solid ratio, etc) and their effects and interactions on grade and yield recovery of final concentrates. Effects of specialized techniques like heavy liquid and wet Frantz analyses will also be studied.

In the magnetic testwork stage, wet high intensity magnetic separation will be studied as a preconcentration process and for cleaning gravity of flotation concentrates. Magnetic selectivity will be determined. Minimization of nonmagnetic entrainment in the preconcentrate. Effects of magnetic field and gradient optimum matrix type, solid liquid ratio will be studied.

The flotation testwork stage will provide information on selectivity and sensivity to water quality and should result in new specification of reagents (several reagents will be experimented on).

The hydrometallurgical testwork stage will evaluate alkaline leaching of wolframite preconcentrates and solution purification techniques. Special emphasis will be given to hydrometallurgical treatment of concentrates obtained by the above mentioned separation techniques (gravity, magnetic, flotation) in order to find routes which will produce concentrates with more than 50% tungsten oxide (threshold mandatory to enter into the market).

Economic evaluation and computer simulation will provide design data for a demonstration pilot plant.

Pilot plant experimentation in batch will demonstrate the practical application of the process to recover 25 micron wolframite with a sufficient yield and grade. Selectivity and sensitivity to process conditions will be assessed at this scale. Based on results obtained during this experimentation it will be decided whether a hydrometallurgy leach pilot plant will be worth while to operate and if so leach plant experimentation will be conducted.

Coordinator

Beralt Tin and Wolfram
Address

6225 Covilhã
Portugal

Participants (2)

INSTITUTO GEOLOGICO E MINEIRO
Portugal
Address
Rua Da Amieira
4465 Sao Mamede De Infesta
Richard Mozley Ltd
United Kingdom
Address
Cardrew
TR15 1SS Redruth