Technical Notes - Minerals Beneficiation - Quantitative Bubble Pick-Up Methods

EFFORTS to obtain definite quantitative data when employing the currently used bubble pick-up method1,2 as a pre-flotation investigation tool led to the adoption of the magnifying mirror method and the microscopic method modifications. Quantitative data obtained by these two methods were converted into bubble pick-up indices and bubble pick-up coefficients. Rough correlations were established between the calculated indices and the results of contact angle testing as well as actual flotation under the same conditions. The basic steps of the magnifying mirror method are as follows: 1—mixing 200 ml distilled water, sized and cleaned mineral particles of approximately 0.5 g, pH regulator, and flotation reagents in a glass beaker; 2—swirling the mineral particles to the center of the beaker to leave a clear circumference; 3—pressing an air bubble against the mineral particles for about 1 sec, and then moving the mineralized air bubble to the clear part of the beaker; and 4—dropping all the attached mineral particles of the air bubble by tapping the bubble holder, and counting the number of the dropped particles by looking at the magnified image in the mirror positioned beneath the beaker. This method is impractical for mineral particles which are transparent in water or finer than 200 mesh. The microscopic method is essentially similar to the above described magnifying mirror method, with the exception that the mineralized air bubble was drawn up into the bubble holder and subsequently discharged onto an externally placed watch glass, where the number of pick-up particles was counted with the aid of a microscope or hand lens. Drying was necessary when the discharged liquid interfered with the counting. The results of the bubble pick-up tests can be simply expressed in the form of the actual count. However, this can be misleading because the number of pick-up particles varies not only with the size of bubble but also with the size of particles. This short-coming is largely remedied by the use of the bubble pick-up index. as calculated from the following equation: PI = (pn/p) 100 [1] in which PI and pn are respectively the pick-up index and the number of pick-up particles under any test conditions, and p is the maximum number of pick-up particles of the same mineral under optimum flotation conditions, with the same size holder and particle. The bubble pick-up coefficient is a term coined to denote the difference between the bubble pick-up index of mineral particles in a liquid and that of the same mineral-liquid mixture plus a chemical reagent at the same pH value. For example, the difference between the pick-up index of a naturally floatable bituminous coal in a solution of water and kerosene and that of the same coal in water alone is a bubble pick-up coefficient. Compared with the contact angle method, the quantitative bubble pick-up method is inferior in accuracy but superior in sensitivity. Other advantages of the bubble pick-up method are that the apparatus can be easily assembled, the mineral sample is conventionally prepared, and the test procedure is relatively simple. References S. R. B. Cooke: The Flotation of Quartz Using Calcium Ion As Activator, Trans. AIME (1949) 184, p. 306. 'G. A. Last and M. A. Cook: Theory of Collector-Depressant Equilibrium at Mineral Surfaces. Paper presented at St. Louis Meeting, AIME (February, 1951).