Application of magnetic separation technology for the processing of a colemanite ore

In recent years, the industrial use and importance of boron compounds has further increased with the potential application of boron as hydrogen carrier in the form of BH4 in the exploitation of hydrogen as clean energy. Boron compounds can be produced from a variety of boron minerals and boronrich brines. Colemanite (Ca2B6O11.5H2O), ulexite (NaCaB5O6(OH)6.5H2O) and borax (Na2B4O5(OH)4.8H2O) are the most important boron minerals of commercial interest. Colemanite is extensively used in the production of boric acid and preferentially in the textile and glass industries where sodium content is often undesirable1. Turkey is the largest producer of colemanite concentrates and boron compounds. In Kestelek plant (Turkey), the colemanite ore produced from open pits is processed to produce saleable colemanite concentrates of 90.000 ton per annually. Processing of the ore (25–35 wt.% B2O3) involves size reduction, screening, washing, scrubbing and handsorting stages to remove clay minerals and hence to upgrade the B2O3 content of the ore to 38–45 wt.%. The treatment process is relatively inefficient since a large amount of tailings is produced with significant boron losses (5–15 wt.% B2O3) and waste management problems associated with the boron release to the environment. Development of more cost-effective, environmentally acceptable and simple processes for the upgrading of the ore is, therefore, required to reduce the boron losses to the tailings. Several alternative processes including attrition-scrubbing/classification2,3, electrostatic separation4, ultrasonic pretreatment5,6, thermal decompositiondecrepitation7-13, flotation14-17 and leaching1822 were extensively studied to recover colemanite from the ore and the tailings. None of these processes apart from attritionscrubbing followed by classification has been further developed due to their inherent shortcomings. To illustrate, slime coating was identified to be the most severe problem, adversely affecting flotation recoveries whereas the thermal treatment methods such as decrepitating are energy intensive. Although aqueous processes using inorganic and organic acids and gas-saturated solutions are attractive, they suffer from high reagent consumption and expensive solid/liquid separation. Magnetic separation is one of the most extensively used separation methods in the mineral processing applications23-25. Weakly magnetic minerals with low susceptibilities (<5 10-6 m3 kg-1)26 could be readily recovered by high intensity magnetic separators, which can generate high magnetic fields (>0.8 Tesla) and field gradients in the orders of 50–500 T m-1. Flores et al.27 reported that, except for ulexite, which had weakly magnetic properties, other boron Application of magnetic separation technology for the processing of a colemanite ore