Mineral Processing Engineering

Each year about 50 million tons of flotation tailings are discarded in Florida phosphate operations. These tailings only contain about 4 pct of the phosphate in the ore; however, over half of the phosphate in the tailings is concentrated in the plus 600-µm size fraction at grades of up to 20 pct P2O5. Many of the phosphate producers have attempted to solve this problem by floating the plus 425-µm flotation feed separately. However, phosphate recoveries in these circuits are typically only 60 pct. For seven sampled phosphate operations, the phosphate content of the plus 600-µm fatty acid tailings ranged from 15 to 25 pct P2O5. In every case the plus 600-µm fatty acid tailings was higher in grade than the overall flotation feed. Attempts to efficiently recover this coarse phosphate have apparently been unsuccessful at these seven phosphate operations. Recovery of this coarse phosphate would provide an additional 0.9 to 2.25 million metric tons of phosphate annually and add an additional year to the reserves of these important deposits.

A typical central Florida phosphate matrix is composed of three different mixtures of minerals. The plus 1-mm portion is chiefly phosphate pebbles

Conventional froth flotation is one of the most widely used mineral beneficiation processes. Unfortunately, long residence times are often required to achieve complete flotation. These slow flotation kinetics have been associated with the hydrodynamics within the flotation cell. While flotation cell manufacturers have optimized the mixing hydrodynamics, little effort has been made to improve the flotation hydrodynamics within the flotation cell.

A conventional flotation cell has both a turbulent region, where bubble-particle attachment occurs, and a quiescent region, where the ore-laden froth is removed from the cell. The flotation rate of a single particle in this environment is a function of the probabilities of bubble-particle collision, attachment, and the motion of the bubble moving into the froth. To increase the flotation rate of a flotation cell, the number of bubble-particle collisions must be increased. One way to increase the number of collisions is to increase the number of bubbles, either by decreasing the bubble size or by increasing the air flow rate to the flotation cell. Unfortunately, the bubble size is limited by the mechanical action in a conventional cell, and at high air flow rates, the mechanical cell’s agitation is

It is envisioned that the utilization of nonpathogenic microorganism and/or extracellular surfactant derived from microorganism as a flotation collector will replace some of the environmentally toxic flotation collectors and at the sometime improve flotation efficiency. The selection screening, and judicious selection of appropriate microorganism as flotation collector has been a challenge to process engineers.

Surface Chemistry of Mycobacterium Phlei

M. phlei is a gram-positive procaryotic cell. It has a rod like shape with 1-1.5 µm in diameter and 5 µm in length. However, the shape can be altered depending on the culture method and rate of growth. Figure 1a shows the Scanning Electron Microphotograph of M. phlei at pH 3.

From the foregoing it can be realized that the surface composition and surface chemistry of M. phlei, in a microscopic scale, resemble to conventional flotation collectors. In this paper, particular attention is focused to elucidate the role of M. phlei as a flotation collector of hematite and to correlate flotation results with bacterial adhesion, hydrophobicity and electrokinetics behavior.

Experimental Materials and Procedure

Hematite samples were hand ground to minus 10 mesh followed by ceramic ball mill grinding to achieve required size