The Process of Froth Flotation - Lab Report Example

This laboratory work aims at aiding us to get familiar with the process of froth flotation. Here, the effect of Collector concentration on the recovery of quartz particles is investigated by measuring the recovery Of particles and determining the flotation rate constant which are crucial parameter in this process. At the ends of this experiment, we aim to achieve the following: 1. To identify the optimum dodecylamine concentration to maximize the recovery of quartz by flotation. 2. To investigate the optimum dodecylamine concentration to maximize the recovery of quartz by flotation. 3. To fit the recovery data obtained assuming a first order kinetic model Introduction The froth flotation method is widely used in the minerals and coal industries to separate the valuable components of an ore from the remaining unwanted materials. In this method, mineral particles are suspended in water to form slurry and selectively attach to air bubbles. The mineral loaded bubbles rise to the surface to form a froth which overflows from the flotation unit. The separation of minerals by flotation takes places in a flotation cell. It is important to understand that the process of separation is very selective and it is regulated by the wetability of the surface which is controlled through the addition of chemical reagents. Collectors are organic molecules which react with the mineral surface to make the surface hydrophobic. Activators and depressants on the other hand promote or delay the absorption of the collector to the mineral surface. Frother is also added to the slurry as a reagent. It is known to have hetropolar organic molecules but unlike collectors, they absorb at the air slum interface. They are used to stabilize air bubbles and the froth phase. Another important class of reagents is PH modifiers. They are used to change the PH of the slurry for which mineral and surfactants are sensitive to. Theory. Froth flotation is a method that is being used widely in the mining industry in processing of minerals. In this process, minerals of economic value are separated from worthless rocky materials or other materials that have some degree of economic value by forcing them to gather on the outer surface of a froth layer. Those minerals that are separable using this technique include both sulfide and non sulfide minerals and also some native metals such as iron. Frothing is based on the ability of certain chemicals contained in the mineral to create some modified properties of the surface of the minerals. While carrying out this process, minerals are crushed and ground to a fine size. This ensures the individual mineral particles are separated. Crushing is carried out in water and a result in slurry. The resulting pulp is then processed in a flotation cell. The ability of a material to float in this process depends on its surface properties. Procedures 1. Materials and sample preparation Use commercial minerals grade 100G silica between 150 and 200 grams of dry quartz is required for each flotation test. The collector used is dodecylamine This is a cationic collector for quartz. Tests are conducted at concentrations in the range 10-5 to 10-4 gmol/L dodecylamine. 2. Flotation Prepare stock solution of 1x10-2 M concentration of dodecylamine in distilled water. Change 150-200 grams of quartz with approximately 4 litres of solution into the 4 litre stainless steel cell of the Denver flotation machine. Lower the mechanism and fill up the cell with water and proper amount of dodecylamine solution to 5 mm from the lip. When performing a run, maintain a constant liquid height inside the cell by adding an additional solution. With the air valve closed, turn on the impeller and adjust the speed to 1000rpm. Allow the contents of the vessel to stir for 10 minutes. To float the solids, open air valve. Collect from the samples at different time intervals into trays and start the stop watch. When the froth overflows, the lip and touches the tray. It may be necessary to gently scrape the froth over the lip but be careful not to carry over too much slurry. Take your reads at intervals of 0-15 seconds, 15-30 seconds, 30-60 seconds, 1-2 minutes, and 2-4 minutes. The end flotation test here has been set arbitrarily at up to 4 minutes. Do the floatation experiment at four different dodecylamine concentrations. After you have completed your experiment, do not forget to clean your work area and all the equipment used. Results and discussion In the experiment we have 4 tests conducted with samples of different concentration. If we analyze the 1 x 10-5 M solution, we have the following: We can perform a similar analysis for all the other four concentration tests to determine the volumes required. After changing the concentration of dodecylamine in the range 10-5 and 10-4 M, the conditions that give maximum recovery were calculated such that: Also to be calculated is the maximum recovery which is obtained by: Figure 1: Tabulated data results DDA Concentration (M) Time (s) Mass Recovered (g) Cumulative Mass Recovered (g) Cumulative Recovery (R) ln[(R∞-R)/R∞] 1 x 10-5 0 0.00 0.00 0.0 0.00 15 7.40 7.40 0.1 1.82 30 4.70 12.10 0.2 0.08 60 8.70 20.80 0.4 0.01 120 14.30 35.10 0.7 0.00 240 18.10 53.20 1.0 0.00 0 0.00 0.00 0.0 0.00 3 x 10-5 15 26.10 26.10 0.2 0.06 30 13.80 39.90 0.3 0.21 60 36.90 76.80 0.6 0.00 120 31.80 108.60 0.8 0.00 240 21.50 130.10 1.0 0.00 6 x 10-5 0 0.00 0.00 0.0 0.00 15 68.10 68.10 0.50 0.00 30 20.90 89.00 0.70 0.00 45 10.60 99.60 0.74 0.00 60 12.00 111.60 0.84 0.00 120 9.80 121.40 0.91 0.00 240 11.50 132.90 1.00 0.00 1 x 10-5 0 0.00 0.00 0.00 0.00 15 80.60 80.60 0.48 2.61 30 23.00 103.60 0.63 0.00 60 27.80 131.40 0.80 0.00 120 19.20 150.60 0.92 0.00 240 13.90 164.50 1.00 0.00 Below are graphs of cumulative recovery time against the time intervals. Figure 1: graph of cumulative time versus time for 1 x 10-5 M Figure 2: Graph of graph of cumulative time versus time for 3 x 10-5M Figure 3: graph of cumulative time versus time for 6 x 10-5 M Figure 4: graph of cumulative time versus time for 1 x 10-5 M From the graphs of the four concentrations of the solution, we can see that the cumulative recovery is proportional to the molar concentration of the fluid up to a certain level where it becomes saturated and then the recovery time becomes a constant in the solution. An analysis of the maximum recovery time data from the table above results in the graphs below: Figure 5: graph of maximum recovery time versus time for 1 x 10-5 M Figure 6: graph of maximum recovery time versus time for 6x 10-5 M Figure 7: graph of maximum recovery time versus time for 1 x 10-5 M From the graphs, an average The flotation follows a klimpel model an this means that the recovery does not reach maximum limit of 100% even at the longest level of flotation time and this can be attributed to: Presence of non liberated particles and also presence of heavy and light materials in the samples. From figure 5 , we can determine the flotation rate constant. From the regression line, point Conclusion From the analysis above, we can conclude that the objectives of the experiment were met. The optimum dodecylamine concentration necessary to maximize the recovery of quartz flotation was determined and their values analyzed. The effect of dodecylamine concentration on the kinetics of quartz flotation was also determine and it was found out that the concentration is proportional to the recovery time until the solution becomes saturated. This test is dependent on the size of particles and therefore large particle are likely to result in poor results. Recommendation It is recommended that during the application of this method in minerals processing, the minerals should be properly crushed to the finest particles possible. The slurry should also be properly mixed to remove any air spaces that may have been left. It is also recommended that the dodecylamine solution used should be highly concentrated to make sure that optimum results are achieved. References D.W. Furstenau, Correlation of contact angles, adsorption density, potentials, and flotation rate, Trans. Am. Inst. Mining Met. Petrol. Engineers, Tech. Publ. 208 (1957) 1365–1367 R.W. Smith, J.L. Scott, Mechanisms of dodecylamine flotation of quartz, Min. Proc. Extractive Metall. Rev. 7 (1990) 81–94. S. Ata, G.J. Jameson, The formation of bubble clusters in flotation cells, Int. J. Miner. Proc. 76 (2005) 123–139. Read More