| Abstract Scope |
Bauxite is the main raw material for alumina production. Bauxites can be karst-type, associated with limestone and dolomite, or lateritic-type, formed from the weathering of silicate rocks. In the Amazon region, bauxite processing plants’ remove the kaolinite through classification steps using hydrocyclones after comminution and scrubbing steps. The fraction smaller than 38 µm (considered fines) tends to follow the tailings stream (hydrocyclone overflow). The reduction of this fraction is necessary to reduce the reactive silica grade on bauxite, which directly impacts refinery operating costs due to the formation of DSP on bauxite digestions, that consumes caustic soda. Kaolinite is a clay mineral that tends to be concentrated in the finer fractions of bauxite (-10 µm). Due to the decline in the quantity of high-grade ores worldwide, the beneficiation of low-grade ores has become increasingly important. However, processing low-grade ores is considered a challenge, as most of them are associated with the presence of ultrafine particles. The study investigates the influence of air flow and wash water rates during a flotation pilot tests using column to promote the concentration of bauxite ultrafine particles (-38+10µm) from tailings generated at Hydro’s bauxite processing plant in Brazil. Approximately 4,000 liters of bauxite tailings slurry were collected at the Hydro’s bauxite processing plant. The sample contained approximately 6% solids by weight. The sample was submitted to desliming process with 3 desliming stages using a small-diameter hydrocyclone. The underflow of the third stage was submitted to flotation using column with dispersant and amide-amine as collector. An analysis of the variation in air and wash water flow was performed via Minitab. The main conclusions were that increasing the air flow rate in the flotation column produces concentrates with a better Al/Si ratio but causes a significant drop in alumina recovery (a drop of approximately 30 percentage points). Increasing the wash water improves alumina recovery, but it is not possible to achieve concentrates with an Al/Si ratio of at least 10. With the higher air flow rate (1.47 L/min) and lower wash water rate (0.12 L/min), it was possible to achieve a concentrate with an Al/Si ratio of 10. The alumina and silica grades were 47.8 and 4.7, respectively. In this test, the alumina recovery was 47%. Considering a cycloning and column flotation circuit, the overall alumina recovery was 13.5%. Through simulation, this recovery level would increase the alumina recovery of Hydro's bauxite beneficiation plant by approximately 4 percentage points, with no negative impact on product quality. |