Seletividade de reagentes na flotação reversa de minério de ferro

Abstract

Froth flotation of ores is a physicochemical process used for selective separation of substances with different surface properties. The induction of this distinguishing property is held by action of reagents that adsorb on the mineral surface of particles and other interfaces present in the process. At cationic reverse flotation, particles of quartz (SiO2) are collected by the action of cationic surfactants, designated as etheramines, while hematite (Fe2O3) is concentrated in the pulp in suspension through depressant action of natural organic polymers such as starch. This work aims to study the influence of reagent types on selectivity of iron ore flotation through use of two collectors/frothers (ethermonoamine and etherdiamine), when used in the presence of three types of corn starches with different contents of amylose and amylopectins, acting as flocculants and depressants. Flotation tests were conducted at bench scale with two fractions of ores from Samarco Mineração, classified as fines (D50 = 20 m) and coarse (D50 = 70 m). The results show that the ethermonoamine is more selective than etherdiamine in flotation of fines, while etherdiamine is more effective for the coarse fraction. In addition, for both minerals tested, ethermonoamine yields lower SiO2 grade in the concentrate, while etherdiamine enhances the metallic recovery of iron. The pH affected significant the selectivity of reagents, showing specific operation ranges for each type of etheramine, in other words, etherdiamine requires higher pH values compared to ethermonoamine. The amylopectin content in starches strongly affected the selectivity of flotation, and starch containing 100% amylopectin presented the maximum Selectivity Index and Separation Efficiency values for both minerals tested. The evaluation of the results allowed the simulatation of optimized process strategies (dosage, pH, collector type and depressant type) for obtaining concentrates with distinct commercial quality specifications (CNS-Concentrate Normal silica and CLS-Concentrate Low silica) and maximum metallurgical recovery for these ore types. The simulation results showed that etherdiamine would be the best collector to obtain CLS concentrates (1,0% < %SiO2 < 1,2%) or CNS (1,8% < %SiO2 < 2,0%) for the coarse fraction, while for fines, the best strategy would be to use ethermonoamine to produce CLS concentrates and etherdiamine to obtain CNS. In all situations, the best results were achieved when the collectors were used together with starch containing 100% amylopectin.