Evaluation of potential processes for the recovery of resource materials from coal residues: Fly ash

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Abstract

This report evaluates potential processes for the recovery of resource materials from fly ash and present preliminary experimental results. Existing processes such as lime--sinter and acid leach for the production of alumina and other resource materials from fly ash were investigated. Also, several new sinter-leach methods were studied; and NaCl-Na{sub 2}CO{sub 3} sinter, H{sub 2}O-acid leach method was found to produce >97% solubilization of aluminum, iron, and a number of trace elements such as titanium, uranium, and manganese. Conceptual process flowsheets were developed for three of the processes that appear to have merit: lime-soda-sinter, salt-soda-sinter--nitric acid leach, and nitric acid leach. Material balances for these processes, based on information available in the literature and from results of our investigations, are presented along with very preliminary cost estimates to be used for comparison purposes only at this stage of development. Cost estimates indicate reasonable agreement in the capital costs for the three plants; however, the operating costs and income from products show significant differences. Income from products is difficult to estimate at this stage of development. Material balances show that the recovery of alumina is {approximately}85, 90, and 65% and the quantity of fly ash consumed is {approximately}90, 60, and 30% for the lime-soda-sinter, salt-soda sinter--nitric acid leach, and the nitric acid leach processes respectively. The lime-soda-sinter process limits product yield to iron, alumina, and cement. The salt-soda-sinter--nitric acid leach and nitric acid leach processes are much more flexible in this regard. In addition to iron and alumina, they are adaptable to produce titanium, silica, and manganese, using solvent extraction methods as shown in our conceptual process flowsheets; various other metals and minerals can also be obtained, depending on the type of process treatment applied. 13 refs., 10 figs., 15 tabs.

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