A review of the beneficiation of calcareous phosphate ores using organic acid leaching

The beneficiation of phosphate ores containing carbonate gangue by conventional techniques such as physical separation methods or flotation is very difficult due to the similarities in physico-chemical properties of constituent minerals present in the system. Carbonate-rich phosphate deposits can be processed by calcination and by selective acid leaching methods. However, calcination has some drawbacks and selective leaching with organic acids is a promising method for the beneficiation of this type of ore.In this paper, the leaching of calcareous phosphate ores proposed in the literature is reviewed with the aim of identifying the important factors involved in the dissolution process. The literature indicates that the organic acid reagent, acid concentration, reaction time, solid/liquid ratio, temperature, particle size distribution and stirring speed are important parameters in the process. The range and optimum values of these parameters reported in the literature are summarized, but there is still some doubt regarding the optimum reaction time. Analysis of the leaching kinetic data and activation energy show that the leaching reaction is chemically controlled.Limited consideration is given to the economic aspects of organic acid leaching. The leaching method appears to be cheap, but a complete economic evaluation is required for each ore, dependent upon the local price of the organic acids used and the cost of their recovery. It is proposed that future research should focus on the leaching characteristics of specific calcareous phosphate ores and on the development of a methodology to optimise leaching using organic acids.