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DESIGN OF COUNTER CURRENT DECANTATION IN COPPER METALLURGY Joseph Kafumbila
Design of counter current decantation in copper metallurgy
© 2016 Joseph Kafumbila jokafumbila@hotmail.com
Joseph Kafumbila
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Content
GENERAL
1.1.PULP WASHING METHOD1.2.CHARACTERIZATION OF PULP1.2.1. SOLID1.2.2. LIQUID1.2.3. PULP
2.
COUNTER CURRENT DECANTATION
2.1.DESCRIPTION OF COUNTER CURRENT DECANTATION2.2.EQUATIONS OF MASS BALANCE INCCD 2.2.1. DESIGNATION OF PULP2.2.2. EQUATIONS OF MASS BALANCE
3.
DESIGN OF COUNTER CURRENT DECANTATION
3.1.PRELIMINARY DATA3.1.1. CHARACTERISTICS OF FEED PULP3.1.2. MIXING EFFICIENCY3.1.3. FLOCCULANT CONSUMPTION3.1.4. WASH RATIO3.1.5. SET VALUE OF CONTROL PARAMETER OF UNDERFLOWS3.2.NUMBER OF THICKENER IN THECCD
4.
SETTLING TEST
4.1.TYPES OF SETTLING TEST4.1.1. RULE THUMB SIZING4.1.2. CYLINDER SETTLING TESTS4.1.3. DYNAMIC THICKENER TEST WORK4.2.CYLINDER SETTLING TESTS4.2.1. EQUIPMENT4.2.2. CHARACTERIZATION OF PULP4.2.3. FLOCCULANT PREPARATION4.2.4. SETTLING TEST4.2.5. SETTLING CURVE4.2.6. SIZE OF THICKENER
5.
5.1.
OPTIMUM NUMBER OF THICKENER IN THE CCD CIRCUIT
OLD METHODSJoseph Kafumbila
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5.1.1. FIRST METHOD5.1.2. SECOND METHOD5.2.NEW METHOD5.2.1. CONSTRAINTS5.2.2. FIRST EXAMPLE5.2.3. SECOND EXAMPLE5.2.4. OBSERVATIONS
6.
6.1.6.2.6.3.6.4.6.5.
7.
PROCEDURE OF CCD CIRCUIT SIMULATION
GENERALPLANT DESCRIPTIONPRELIMINARY DATA OFCCDCIRCUITSIMULATION TABLEPROCEDURE OFCCDCIRCUIT SIMULATION
REFERENCE
Joseph Kafumbila
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Foreword The counter current decantation had been used since 90 years ago in the hydrometallurgical plant. It is currently adopted by all new hydrometallurgical plants located in the Katanga Province of the Democratic Republic of Congo (Ruashi Mining, Mumi Mining etc.) since it is applicable to all products; but its malfunction can limit the production of the plant. This publication is an upgrade of the publication called “Initiation à la simulation des flowsheet” andgives the procedure of CCD circuit design in the simplest way. In the first chapter, the pulp is characterized using three parameters (mass, volume and specific gravity). This publication gives the mathematical expressions that link the three parameters for the two constituents of the pulp (solid and liquid) and for the pulp. Specially, this publication gives the simplest method to determine the specific gravity of solid when the mineralogical composition of solid is available and the specific gravity of liquid when chemical composition liquid is available. In the second chapter, this publication gives the description of CCD circuit and the mass balance equations of thickener and CCD in the steady state condition. The difference with the first publication “Initiation à la simulation des flowsheet”, theflocculant is considered a solid. In the third chapter, this publication gives the preliminary data to have before the design of the CCD circuit and the method for obtaining the value of these preliminary data (the mixing efficiency, the flocculant consumption, the wash ratio and the set value of the control parameter of underflows). In the fourth chapter, this publication gives the procedure of the cylinder free settling test. The purpose of this chapter is to give the simplest method for obtaining the flocculant consumption and sizing the thickener. In the fifth chapter, this publication gives the old and new methods for obtaining the optimum number of thickeners in the CCD circuit. In the new method, the determination of optimum number of thickener is illustrated through two examples using the conventional thickener and the High Rate Thickener. The last chapter gives the procedure of simulation of CCD circuit with the new method on an Excel spreadsheet through the example.
Joseph Kafumbila
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1.General 1.1.Pulp washing method Pulp washing in the CCD is part of the pulp wash process. The pulp wash process is a special operation that performs both the extraction and the solid - liquid separation. Thus the pulp wash process falls within the category of mass transfer operations for chemical and metallurgical engineering [1]. There are two main kinds of pulp wash techniques: Wash by dilution: the thickened pulps are, at the entrance of various stages, diluted with corresponding wash solutions to achieve such a perfect mixture as possible. The subsequent solid - liquid separation is generally done by decantation. Such washes technique is suitable for the muddy pulp formed of very fine particles. Wash by displacement: the impregnation solution of pulp to be washed is generally removed by the wash solution, which is substituted directly to it more or less complete. This kind of wash technique is suitable for the permeable grainy pulp. The solid - liquid separation is usually achieved by filtration or draining. By dilution or by displacement, the pulp wash technique can be done in two main ways: Split wash or cross flow Methodical wash or counter current In what follows, it will be treated the pulp wash in the CCD since it is more effective and widely used in the metallurgical industry of Copper. 1.2.Characterization of pulp Generally, the suspension of particles in a solution is called pulp. The suspended particles will be called solid and form the solid phase while the impregnation solution is the liquid phase. Therefore, the pulp will always consist of two components: solid and liquid. It will be discussed first the characterization of the two components of pulp before the characterization of pulp. The characterization means, in this publication, the designation of important parameters of a phase and the development of equations linking these parameters.
Joseph Kafumbila
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1.2.1.Solid 3 The solid is characterized by a mass (M) expressed in (kg) and a volume (V) expressed in (m ). The ୱ ୱ 3 specific gravity (SG) expressed in (kg/m ) is the ratio of the mass onto the volume of solid. Equation (1) gives the mathematical expression that links the mass, the volume and the specific gravity of solid. ŝ SG= ŝ(1) v The solid is considered insoluble in the CCD circuit and the specific gravity of solid is constant. There are two methods for obtaining the specific gravity of solid: the laboratory method and the mineralogical composition method. A.Laboratory method When it is possible to have physically the solid, the laboratory method for obtaining the specific gravity of solid consisting of mineral rock finely crushed is as follows: Dry the crushed solid in an oven at 80 ° C for 24 hours, Weigh the solid (kg) (weight between 0.100 and 0.300 kg), Put the solid in a test tube of one liter, Add the water in the test tube up to 500 ml, Mix the solid and the water until complete homogenization, Add more water in the test tube to the mark of a liter and, Weigh the volume of one liter of pulp. After the practical operations, the other data is determined as follows: The weight of water is the difference between the weight of pulp and the weight of solid. 3 The volume of water is the ratio of weight onto the specific gravity of water (1,000 kg/m ). The volume of solid is the difference between the volume of pulp and the volume of water. Finally, the specific gravity of solid is the ratio of the weight onto the volume of solid. Table (1) shows an example for obtaining the specific gravity of solid by the laboratory method. This method seems simple, but it requires great accuracy during the weighing and the measuring of values. Table 1: Specific gravity of solid from the laboratory method Description Units Equations values Weight of solid kg 0.141 Weight of pulp kg 1.089 Volume of pulp l 1.000 Weight of water kg Weight of pulpWeight of solid 0.948 Volume of water l Weight of water/specific gravity of water 0.948 Volume of solid l Volume of pulpvolume of water 0.052 SG of solid kg/m3 Weight of solid/volume of solid*1000 2,711.54
Joseph Kafumbila
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B.Mineralogical composition method When the solid is not provided in order to obtain its specific gravity by the laboratory method, the determination of specific gravity of solid is taken place by using the mineralogical composition method. This method is based on the principle that rock is a juxtaposition of minerals. Therefore, the mass of rock is the sum of masses of minerals and the volume of rock is the sum of volumes of minerals. Based on these assumptions, the method for obtaining the rock specific gravity consists of: Knowing the weight percentage of minerals in the solid. Calculating the weight of minerals in a unit mass of solid. Knowing the respective specific gravity of minerals. Calculating the volumes of minerals. Determining the volume of solid by the addition of volumes of minerals. Calculating the specific gravity of solid by using the equation (1) The weakness of this method is that it ignores porosities or structural defects of solid. Table (2) shows an example for obtaining the specific gravity of solid by using the mineralogical composition method. The result from Table (2) shows that for a total weight of 1,000 t of solid and a total volume of 3 359.77 m of solid which is the sum of volumes of minerals, the value of specific gravity of solid is 2,779.55 3 kg/m . Table 2: Specific gravity of solid from the mineralogical composition Minerals Grade weight Specific gravity Volume of Specific gravity of mineral mineral of solid 3 3 3  % t t/m m kg/m Cu2(OH)2(CO315.836 4.00 ) 1.584 3.959 Cu3(PO4)2.Cu2(OH)4 0.146 1.456 4.20 0.347 2CuO.2SiO2.3H2O 0.199 0.9041.989 2.20 CuO 0.503 5.029 6.40 0.786 CuS 0.005 0.055 4.68 0.012 Cu2S 0.005 0.055 5.65 0.010 CuFeS20.0130.055 4.20  0.005 CoOOH 0.507 5.070 4.00 1.268 FeO(OH) 1.954 19.543 3.65 5.354 Ni(OH)20.002 0.001 0.010 4.10 CaCO3.MgCO33.1589.000 2.85  0.900 MnO2 0.127 1.266 4.85 0.261 ZnS 0.007 0.067 4.00 0.017 SiO2771.393 2.65  77.139 291.092 UO3 0.004 0.0040.040 10.97 Mg2SiO4 5.381 53.805 3.15 17.081 Ca2SiO4 0.011 0.110 2.71 0.041 CaCl20.1160.250 2.15  0.025 Al2SiO5114.710 3.25 35.295 11.471 Cr2O30.0490.256 5.22  0.026 CdO 0.001 0.006 8.15 0.001 Total 1000 359.77 2,779.55
Joseph Kafumbila
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1.2.2.Liquid 3 The liquid is characterized by a mass (M) expressed in (kg) and a volume (V) expressed in (m ). ୐ ୐ 3 The specific gravity (SG) expressed in (kg/m ) is the ratio of the mass onto the volume of liquid. Equation (2) gives the mathematical expression that links the mass, the volume and the specific gravity of liquid. L SG= v L(2) There are two methods for obtaining the specific gravity of liquid: the laboratory method and the chemical composition method. A.Laboratory method When it is possible to have physically the liquid, the laboratory method for obtaining the specific gravity of liquid is as follows: Put the liquid in a test tube of one liter to the mark of a liter, Weigh the volume of one liter of liquid (g), And the ratio of weight onto the one liter volume of liquid gives the specific gravity. The specific gravity obtained in this condition is the approximated value at ambient temperature. B.Chemical composition method A liquid is homogeneous mixture of solvent and solutes. In this publication, the solvent is water and solutes are the elements appearing in the metallurgy of Copper and dissolved in water as sulphate. These elements appearing in the metallurgy of Copper are listed in the Table (3). The Sodium is on the list since it may come from sodium metabisulfite used as a reducing agent during leaching of trivalent Cobalt. The phosphoric acid comes from pseudo malachite. The index “k” is an identification number of the chemical elementin this publication. At this level, it is defined two other parameters; the mass of element of index “k” (M) expressed in (kg) in the liquid and the k 3 concentration of element of index “k” (C) in the liquid. Equation (3) gives the) expressed in (kg/m k mathematical expression that links the mass of element of index “k”, the concentration of element of index “k” and the volume of liquid.M=VxCk ୐ k (3) It has been observed for a liquid containing copper sulphate and sulphuric acid that [2]: The specific gravity of copper sulphate or sulphuric acid liquid is approximately a linear function of concentration expressed in (%). The specific gravity of liquids of equal concentration expressed in (%) of copper sulphate and of sulphuric acid is nearly identical. The specific gravity of liquid containing appreciable amounts of copper sulphate and sulphuric acid is dependent principally upon the total concentration (%) and is almost independent of their proportion. Joseph Kafumbila Page 8
These observations have been extended to the elements appearing in the Copper metallurgy and the simplest method that allows having the approximated value of specific gravity of liquid from the chemical 3 composition is given. The method consists of finding a total concentration (C) of) expressed in (kg/m elements as salt in the liquid. In this case, the salt is in form of sulphate except the phosphoric acid. After, the total concentration must be applied in the equation (4) which gives the relation between the liquid specific gravity and the total concentration of elements. The equation (4) comes from data which give the specific gravity of liquid as a function of concentration of element as salt in binary system [3]. Table 3: Elements appearing in metallurgy of copper Element Index (k) H2SO4 1 Cu 2 Co 3 Fe 4 Zn 5 Ni 6 Mn 7 Mg 8 Al 9 Ca 10 Na 11 Cr 12 Cd 13 H3PO4 14 3 −ସ ୱ ଶ ୱ SG= -6.139 xͳͲx[C ]+ 0.9742 xC+ 1000 (kg/m ) ୐ ୲ (4) Therefore, it is defined a constantȽof element of index “k”. TheconstantȽis the value to k k multiply to the concentration of element indexkto have the concentration as sulfate saltC. The values k of constantare given in Table (4).The value of concentration “C” of element of index “k” is given by � k equation (5). C=ȽxCk k k (5) Table 4: value of constantElément Index (k)Ƚk H2SO41.000 1 Cu 2 2.511 Co 3 2.629 Fe 4 2.719 Zn 5 2.468 Ni 6 2.635 Mn 7 2.747 Mg 8 4.949 Al 9 6.337 Ca 10 3.395 Na 11 3.088 Cr 12 3.769 Cd 13 1.854 H31.000PO4 14
Joseph Kafumbila
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Thus, the value of total concentration “C” of elements in the liquidwill be calculated according to equation (6). ୱ k ୱ k C=∑ C=x C∑ Ƚ ୲ ଵ k ଵ k k (6) Table (5) gives an example for obtaining the specific gravity from the chemical composition of given liquid. The result of Table (5) shows that the value of total concentrationC” of elements in the liquid is 3 97.251 kg/m . This value is the sum of concentrations as sulphate salt of elements. By applying the value of total concentration of elementsin the equation (4), the value of specific gravity of liquid “SGis 1088.94 3 kg/m . It is important to have ten major elements so that the calculated specific gravity of liquid will be closed to the true specific gravity. Table 5: Specific gravity from chemical composition of liquid Element Index (k) ConcentrationȽCk k  kg/m3 kg/m3 H2SO44.956 1.000 4.956 1 Cu 2 4.670 2.511 11.725 Co 3 11.233 2.629 29.532 Fe 4 2.925 2.719 7.954 Zn 5 0.099 2.468 0.244 Ni 6 0.000 2.635 0.000 Mn 7 2.812 2.747 7.724 Mg 8 4.440 4.949 21.974 Al 9 1.474 6.337 9.341 Ca 10 0.455 3.395 1.543 Na 11 0.000 3.088 0.000 Cr 12 0.108 3.769 0.407 Cd 13 0.001 1.854 0.002 H3PO4 14 1.849 1.000 1.849 C 97.251 1.2.3.Pulp The pulp is a mixture of solid and liquid. The pulp will be characterized by a mass “M” expressed 3 3 in (kg), a volume “Vexpressed in (m ) and a specific gravitySGexpressed in (kg/m ). Equation (7) gives ୔ ୔ the mathematical expression that links the mass, the volume and the specific gravity of pulp. P SG= v P(7) The mass of pulp is the sum of masses of solid and liquid. The mathematical expression of this principle is given by equation (8). M=M+M୔ ୗ ୐ (8) The volume of pulp is the sum of volumes of solid and liquid. The mathematical expression of this principle is given by equation (9).
V=V+V୔ ୗ ୐
Joseph Kafumbila
(9)
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