Colemanite ore purification in a magnetic pulley separator

HORACIO R. FLORES; SILVANA K. VALDEZ; LEUNG H. KWOK

Handbook on Borates: Chemistry, Production and Applications

Nova Science Publishers

Lugar: New York; Año: 2009; p. 421 - 430

The borates with more commercial importantance in the northwest of Argentina are colemanite, hydroboracite, ulexite and tyncal. They present diamagnetic properties, which makes them different from the gangue. Magnetic separation has two possible applications: the first one is the concentration or upgrading the B2O3 content; the second one is the purification by removing the iron or arsenic paramagnetic impurities. Concentration by magnetic separation can not compete with the simplicity and the economy of concentration by crushing and size classification. This profitable technique separates the borates into the bigger sizes and the gangue into the finer ones. This chapter presents the results obtained when a pre-concentrated colemanite sample was purified by magnetic separation. The separation was done by passing the sample through a magnetic field created by a magnetic Nd-B-Fe pulley. Non-magnetic fraction (concentrated colemanite) presents 0.2 % Fe (total iron), which meets the strict commercial specifications of the borate market. Besides, this fraction is scarcely upgraded (between 0.7 and 3.3 %B2O3). The magnetic fraction (tailing) has an important grade of B2O3 (about 25%). These two effects can be the result of an association between the non-magnetic colemanite and the magnetic impurities. To reduce the B2O3 content in tail it would be necessary more crushing, but it could be negative considering the relationship between the borate liberation size and optimum particle size in magnetic separation. Size characterization, specific weight and magnetic susceptibility data of feeding and the products obtained, as well as magnetic field and its gradient measurements, were used to calculate the optimum separation angle for colemanite purification and the forces acting over the particles when they pass through the magnetic zone. It was found that the separation angle is the most important operating variable. Data were collected at a given belt rate. 2O3 content; the second one is the purification by removing the iron or arsenic paramagnetic impurities. Concentration by magnetic separation can not compete with the simplicity and the economy of concentration by crushing and size classification. This profitable technique separates the borates into the bigger sizes and the gangue into the finer ones. This chapter presents the results obtained when a pre-concentrated colemanite sample was purified by magnetic separation. The separation was done by passing the sample through a magnetic field created by a magnetic Nd-B-Fe pulley. Non-magnetic fraction (concentrated colemanite) presents 0.2 % Fe (total iron), which meets the strict commercial specifications of the borate market. Besides, this fraction is scarcely upgraded (between 0.7 and 3.3 %B2O3). The magnetic fraction (tailing) has an important grade of B2O3 (about 25%). These two effects can be the result of an association between the non-magnetic colemanite and the magnetic impurities. To reduce the B2O3 content in tail it would be necessary more crushing, but it could be negative considering the relationship between the borate liberation size and optimum particle size in magnetic separation. Size characterization, specific weight and magnetic susceptibility data of feeding and the products obtained, as well as magnetic field and its gradient measurements, were used to calculate the optimum separation angle for colemanite purification and the forces acting over the particles when they pass through the magnetic zone. It was found that the separation angle is the most important operating variable. Data were collected at a given belt rate.