ALUNITE BENEFICIATION

JIANN-YANG HWANG, Purdue University

Abstract

Alunite, Kal(,3)(SO(,4))(,2)(OH)(,6), is the most promising domestic resource which in the future may substitute for bauxite. Quartz and alunite are the major constituents of these ores. Because of their intimate intergrowths, complete liberation of the two minerals is accomplished at a grain size of about 10 (mu)m. The aim of the present study is to provide a method to remove quartz from alunite or from aluminum hydroxide. The latter is the decomposed product of alunite, and is an intermediate step in the thermochemical, so called Alumet process. Effective removal of quartz might drastically reduce the high capital costs of the plant. A selective seeding method was designed in which selective flocculation and high gradient magnetic separation procedures were combined. This method is analogous to conventional flotation but the air bubbles used in flotation were substituted by magnetite seeds. The selectivity in bonding magnetite seeds to certain minerals was attained by a selective flocculation technique, which is effective for particles smaller than 40 to 50 (mu)m. Magnetic separation can be employed at the low magnetic field strength of 1 kilogauss in a high gradient magnetic filter. The flocs were repeatedly disintegrated and reformed to release the entrapments. The added magnetite seeds were recovered at the run termination by disintegrating the flocs and then magnetically collected. The experimental results proved the viability of the selective seeding method by showing that the quality of separation is a function of dispersant, depressant, flocculant, particle size, solid contents, and deleterious ions in the system. About 3 lb/ton sodium carbonate, 3 lb/ton sodium tripolyphosphate and 0.25 lb/ton "Superfloc 16" flocculant were required in a slurry containing 20% solids with particle sizes between 20 and 2 (mu)m. Alunite was concentrated to 90% grade with 80% recovery after multiple runs. Magnetite seeds were added at the rate of 1 wt% of the ore and were recovered at about 90% purity with 80% yield at the termination of the experiment. Aluminum hydroxide was upgraded from 40% to 80% with 87% recovery from mechanical mixtures of pure minerals. Sodium sulfide, sodium fluoride, and "Superfloc 208" were used as dispersant, depressant, and flocculant, respectively. This approach which is suited for alunite ore does not work well on roasted and leached alunite ore due to activation of quartz during the roasting and leaching procedures.

Degree

Ph.D.

Subject Area

Geochemistry

COinS