Bubble Pick-up Method

Bubble Pick-up Method T.J.F.Dy Echo Department of Mining, Metallurgical and Materials Engineering University of the Philippines, Diliman [email protected] Abstract The Bubble Pick-up Method is a pre-flotation test used to determine if mineral to bubble attachment occurs for a given criteria. This method uses an induced bubble which is pressed on settled minerals in a mixture. In this experiment, the retrieved concentrate from the panning stage of the gravity concentration experiment was subjected to the test method using 46.1μL of potassium amyl xanthate collector, and a drop of NasFroth frother. The experiment provided an average value of 66.6065 chalcopyrite grains collected per square millimeter of bubble surface.

1. Introduction One of the most widely used separation processes in mineral processing is flotation. In this process, several factors are checked upon to ensure effective mineral recovery. Due to high costs that come with actual testing, laboratory-scale methods have been devised to be done prior. The bubble pick-up method is one of the said preflotation tests. This test makes use of induced bubbles pressed down on particles contained in a mixture. The method aims to determine the activity present in the mineral-bubble interface. In the bubble pick-up method, it is determined whether the bubble created is able to successfully lift the desired grains. Other flotation tests are being used in today’s optimization of flotation lines. An example would be the Hallimond cell, a flotation microcell which injects air bubbles (at point A shown below) through mineral slurry.

A modification of the Hallimond cell, done by Siwek and company, is more often used due to certain advantages it provides. One of the most notable is its ability to to test slurries at a wider range of pulp density. The original Hallimond cell is restricted to slurries of only 1 percent solids. For this experiment, the bubble pick-up method was performed to demonstrate the interaction at the mineral-bubble interface. The sample used was the concentrate recovered from the panning stage of the gravity concentration experiment, and was at 100mesh passing.

2. Methodology 2.1 Sample Preparation Before the experiment proper, five grams of the concentrate collected from the gravity concentration experiment was weighed and placed in a 50-mL beaker. It was then diluted to 30mL, subjected to an ultrasonic cleaner for three minutes, then decanted. This cleaning process was done three times, and then the sample was air-dried. Given that the bubble pick-up method is a downsized simulation of flotation, the use of the cleaner for slime removal was necessary. These slimes tend to compete with the valuable minerals for collector attachment. Consequently, a decrease in recovery would be highly possible.

2.2 Bubble Pick-up

Figure 1. Hallimond cell. (photo courtesy of Ramachandra Rao) This cell provides information on the amount of mineral that may be recovered (at point D-E) with respect to bubble stability. With the Hallimond cell, the height to which bubbles start to burst may be recorded, and thus frother dosage may be adjusted.

The air-dried sample was diluted to 50mL. After adding 46.1μL of potassium amyl xanthate (PAX) collector, the mixture was allowed to condition for five minutes. A drop of frother (NasFroth) was then added, and the mixture conditioned for another 30 seconds. An ordinary dropper was dipped into the mixture, and used to induce a small bubble. The created bubble was allowed to touch the settled solids for particle attachment. The said bubble was then transferred onto a glass slide. After three (or four, TJFDyEcho. Bubble Pick-up Method. Page 1 of 3

depending on the number of group members) bubbles have been transferred, the glass slide was viewed under a microscope. Photographs of the magnified bubbles were then recorded as data.

2.3 Particle Analysis (Jeffries Planimetric Method) For the photograph analysis, the Jeffries Planimetric Method was used. This method determines the number of grains found in a given surface area, NA. The method was done by imposing a circle of known diameter on the micrograph. The number of grains within the circle was then counted, with those at the boundary counted as a half. The N A value was then calculated using the equation below (Equation 1) where N = total grain count f = Jeffries factor The value for the Jeffries factor, f, is determined by the equation below Figure 2. Bubble micrographs. (Equation 2) where M = linear magnification AC = area of imposed circle (mm2) The NA value for each bubble was calculated, and then compared.

3. Results and Discussion A total of three bubbles were analyzed in this paper. The figures below show the collected micrographs of the said bubbles.

Following the Jeffries Planimetric Method, a circle was imposed on each micrograph. Since the microscope magnification is unknown, the area of the circle was calculated and adjusted with respect to the given scale. With a diameter of 444.44μm, each superimposed circle was determined to have an area of 0.15514mm2. The yellow grains, considered to be chalcopyrite, enclosed in the circles were counted and recorded as shown in the table below. Table 1. Grain count. Micrograph 1 2 3

Grain Count 10.5 10.5 10

The data above shows very minimal difference between the recorded grains for the designated area per bubble. It must be noted, however, that human error plays a significant role in this experiment’s data collection. The experimenter must be successful in properly inducing the bubble, and in transferring it onto a glass slide. Unnecessary spreading of the bubble on the slide must be hindered, so as to prevent consequential spreading of the attached grains. This will have an effect on the calculations for the N A value, especially since the induced bubble diameter is unknown. The table below shows the calculated N A values for each micrograph.

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Table 2. Grains per unit surface area. Micrograph NA (grains/mm2) 1 67.6808 2 67.6808 3 64.4579 Average 66.6065 The calculated NA values show a relatively large amount of grains per said area. Such data are considered in determining the degree of mineralbubble attachment. Sequential bubble pick-up tests with varying levels of collector and/or frother will provide information necessary for the optimization of reagent dosage during flotation. The given data may be considered more useful if the grain size is known. The Jeffries Planimetric Method denotes that the grain size may be determined by getting the reciprocal of the N A value. It is however not considered applicable for the bubble pick-up method. By looking at the micrographs, it is apparent that the described area is not purely chalcopyrite, and has unoccupied regions. Also, the chalcopyrite particles attached have varying sizes (no definite dimension). This is because the only limit imposed on the particles was to be at 100mesh passing (feed was from mesh-of-grind experiment, assigned 100mesh). If the grain size is known, the comminution process of the ore may also be optimized. The ore may be ground to a size wherein the attachment density capacity of the bubble may be maximized. The amount of additional frother may also be determined, so as to increase bubble stability for larger particle sizes. Another information that may be gathered from the micrographs is the apparent selectivity of the collector used. By looking at the micrographs, a rather large amount of gangue materials were also collected. With this information, experimenters may also deduce the appropriate collector reagent for a desired mineral. It is noted, however, that the addition of lime for pH adjustment was not done during experimentation. As such, the PAX collector selectivity may have substantially decreased.

concept of bubble stability when dealing with coarser particles.

References [1] Dobby, G. S, and S. Ramachandra Rao. Processing Of Complex Ores. New York: Pergamon Press, 1989. Print. [2] Rao, S. Ramachandra, and Jan Leja. Surface Chemistry Of Froth Flotation. Dordrecht: Kluwer Academic/Plenum, 2003. Print. [3] Vander Voort, George F. Metallography--Past, Present, And Future. Philadelphia, Pa.: ASTM, 1993. Print. [4] Vander Voort, George F. Metallography, Principles And Practice. Materials Park, OH: ASM International, 1999. Print.

4. Conclusion The experiment determined an average of 66.6065 grains attached per square millimeter of bubble surface. This value represents a rather high attachment density. The data, however, is insufficient to provide concrete conclusions. In order to acquire a more accurate particle size, it is recommended that the feed ore be sieved between two meshes (rather than simply assigning a single mesh passing). It is also recommended that the setup be done at varying collector and frother dosages. This will allow students to see the relationship between collector amount and recovery. Also, it will demonstrate the TJFDyEcho. Bubble Pick-up Method. Page 3 of 3