操作条件变量对铝颗粒浮选的影响.PDF

118 Chem. Eng. Technol. 14 1991 118- 121 Effect of Some Operating Variables on the Flotation of Aluminium Particles Mohamed S.E. Abdo and Amina M. Darwish The effects of impeller speed, air flow rate, cell concentration, agitator size and cell volume on the recovery of aluminium particles have been studied in a KHD Humboldt Wedge AG machine, using alkyl benzene sodium sulphonate paste as collector and pine oil as frother. The recovery yield increased with increasing impeller speed, air flow rate, cell concentration and cell volume, up to a certain range, whereafter it decreased. A decrease in the recovery yield was observed on increasing the agitator size. A mathematical model has been developed to correlate percentage recovery with the above variables. 1 Introduction Flotation is a process of solid liquid separation, whereby solids are removed from suspension by means of air bubbles. In flota- tion, aggregates of particles and bubbles, with densities lower than that of the suspension, rise to the surface and are removed. The attachment of solid particles to air bubbles depends on the wettability of these particles. The wettability of any material is determined by the physico-chemical properties of its surface [ 1 11. Addition of various agents which are selectively absorbed on the surfaces of certain species in a mixture, can enhance the relative wettability of these surfaces [8]. Flotation agents can be classified into three main categories according to their function, namely collectors, frothers and modifiers [1, 2, 6, 8, 9, 111. Collectors are organic compounds which become absorbed on material surfaces, covering them partially with a film which is water-repellent. The main function of frothers is to produce froth, just stable enough to facilitate the transfer of floated material from the cell surface to the collecting launder [ 1 11. Modifiers are reagents which alter the chemical nature of material surfaces in order to promote or inhibit the collector action. The reagents used in this study were alkyl benzene sodium sulphonate paste as collector and pine oil as frother for the flotation of aluminium scrap. It has been determined previously [ 101 that aluminium particles are easily floated with xanthate- type collectors, after conditioning with a copper solution. 2 Experimental The laboratory tests were carried out with a KHD Humboldt Wedge AG batch flotation machine, type MN 93515. The material to be floated consisted of aluminium scrap particles with sizes between 0.5 and 1 111111. Prior to flotation, the feed pulp was conditioned in the cell. 49.7 g of aluminium particles and 300 ml distilled water were introduced into the cell. At this stage, a certain quantity of chemical reagents collector, * M.S.E. Abdo and A.M. Darwish, Department of Chemical Engineer- ing, Faculty of Engineering and Petroleum, Kuwait University, PO Box 5969, 13060 Safat-Kuwait. frother were measured by a pipette and added to the condition- ing pulp. The impeller speed was adjusted to 1500 min- and a 0.5 min conditioning period was allowed. 650 ml of distilled water were then added, air supply and stopwatch started simultaneously, and the froth was collected during a flotation period of 2.5 min. Water was added during the test to maintain the pulp at a constant level, 2 cm below the overflow weir. The froth was filtered through a porous filter paper, and dried over- night in an oven at 160 “C. The tailings were left to settle. The supernatant liquid was decanted and tailings were dried in an oven. The froth and tailings were weighed and their masses recorded. Details of typical flotation test conditions are listed in Table 1. Investigated Variables. The variables investigated in this study, were air flow rate, impeller speed, cell concentration, cell volume and agitator size. The same procedure was follow- ed in all these experiments, except for changing one of the variables within a given range while keeping the other variables constant. 3 Results and Discussion 3.1 Effect of Cell Concentration Flotation tests were carried out for different cell concentra- tions. Fig. 1 shows that the percentage recovery increases with Table 1. Experimental details of a typical flotation test. Mass of aluminium Mass of pulp Feed pulp concentration Particle size Frother addition Collector addition Impeller speed Aeration rate Nominal cell volume Agitator diameter Constrained froth height Conditioning time Flotation time Initial temperature Final temperature pH range 49.1 g 1000 g 0.05 0.5- 1 mm 0.05 g/kg solids 0.3 g/kg solids 1500 min- 60 I/h I I 5 cm 2 cm 0.5 min 2.5 min 25 “C 27 “C 7-8 VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1991 0930-7516/91/0204-0118 03.50 ,2510 Chem. Eng. Technol. 14 1991 118- 121 119 w Impeller speed [min-I; Q Particle density [g/cm3] 2.74 g/cm3 for aluminium; p Pulp viscosity [g/cm s] 1.4 X 10- g/cm s; t Flotation time [min]; Q Air flow rate [l/h]; V Cell volume [l]; S Cell concentration [g solids]; Re [D2we/p] Reynolds number; WT wt speed number; QN2 [Q / wD3] air flow number; VD V/D3 size number. The exponents a, b, c, d and e as well as the coefficient A are determined by applying the least squares technique. All calcula- tions were carried out on an IBM computer, using statistical graphical system, version 2. Values of the exponents, the coef- ficient A, their standard errors, t-values, significance levels 100 1 / o Agit. Size 9 crn 0 1 2 3 4 5 6 7 Cell Volume I Fig. 5. Effect of cell volume on recovery for different agitator sizes. and probability levels are presented in Table 2. These data cover the intermediate ranges of variables as follows w V/D 0.2 - 0.86 l/cm; t 0.5-4 min. 1000 - 2000 min- ; Q 20-60 I/h; s 0.01 -0.1; The table shows clearly that the WT group has a high level of significance and p-value which means that there was only a marginal contribution by this group to the regression calcula- tion and it should be omitted. The regression equation may, therefore, be modified to R A[ReQN2CVDdSe] . 2 The resultant exponents, coefficient A and all the statistical factors for these are presented in Table 3. In order to test the validity of these Eqs 1 and 2, the values of R-square and standard error of estimation were computed and found to be almost the same for the two equations. The R-square value equals to about 85 and standard deviation to 5.6. The plots of predicted versus observed values are shown in Fig. 6. As shown in the diagram, the points are unily distributed around the diagonal which indicates that the model is satisfactory. Table 2. Values and statistical data of exponents and coefficient in Eq. 1 for intermediate ranges of Q and w. Values Std-error -Value Sig-level p-Value A 4.35 0.503 2.926 0.0053 0.oooo a 0.355 0.049 7.19 O.oo00 0.0ooo b 0.058 0.038 I .54 0.1310 0.177 c 0.127 0.033 3.88 0.0003 0.0002 d 0.179 0.035 5.17 O.oo00 0.0000 e 0.505 0.037 13.85 o.ooo0 0.0000 Chem. Eng. Technol. 14 1991 118- 121 121 Table 3. Values and statistical data of exponents and coefficient in Eq 2 for intermediate ranges of Q and w Values Std-error t-Value Sig level p-Value - - A 5.808 0.473 3.7183 0.0005 - u 0.3686 0.0492 7.487 0.0000 0.0000 c 0.124 0.03305 3.75 0.0005 0.0003 d 0.182 0.0351 5. I95 0.0000 0.0000 e 0.504 0.03699 13.621 0.0000 0,0000 10 20 30 40 50 60 70 80 90 lo0 110 120 Predicted Values Fig. 6. Percentage recovery R for intermediate ranges of Q and w. 5 Conclusions Based on the data presented in this study, optimum ranges of the studied variables can be specified as follows - Cell concentration 5 - 10 wt-; - Impeller speed 1000-2000 min-; - Air flow rate 40 - 60 lih for one litre cell volume; - Cell volume 0.6-0.8 1 per centimetre of agitator diameter. Above and below these ranges, a decrease in percentage recovery has been observed. Application of the proposed Eq. 2 for intermediate ranges of air flow rate and impeller speed leads to very satisfactory results. Received January 29, 1990 [CET 2791 References [l] Aplan, F.F., in R.E. Kirk, D.F. Othmer, Encyclopedia of Chemical Technology, Vol. 10, John Wiley, New York 1980. [2] Atwood, A.L., in R.E. Kirk, D.F. Othmer, Encyclopedia of Chemical Technology, Vol. 7, John Wiley, New York 1983. [3] Degner,V.R.,AZChESymp. Ser. 711975No. 151,pp.257-265. [4] Jowett, A., Chem. Eng. London 1979 No. 34718, pp. 603-607. [5] Krishna, D.M., Indian J. Technol. 16 1978 pp. 347-350. [6] Leja, Jan., Surjiace chemistry offroth jotation, Plenum Press, New York 1982. [7] Lynch, A.J., Johnson, N.W., Manlapig, E.V., Shorne, C.G., Mineral and Coal Flotation Circuirs, Elsevier, Amsterdam 1981. [8] Perry, R.H., Green, D., Chemical EngineerS Handbook 6th edition. McGraw-Hill, New York 1984. [9] Pryor, E.J., Mineral Processing, Elsevier, Amsterdam 1974. [lo] Soto, H., Toguri, J.M., ConservationandRecycling 91986 No. 1, [l 11 Wills, B.A., Mineral Processing Technology, Pergamon Press, Ox- ford 1981. pp. 45-54.