Preliminary study of oxide copper fine particle agglomeration at a laboratory scale

Kássio S. Santos, Luciana de C. Maia, Bruno S. Mosso & Ailton P. Souza Faculty of Environmental and Mining Engineering, Universidade Federal do Pará, Marabá, Brazil, Graduaing of Environmental and Mining Engineer, kssio_01@hotmail.comFaculty of Environmental and Mining Engineering, Universidade Federal do Pará, Marabá, Brazil, Graduate of Enviromental and Mining Engineering, lucianacmaia@hotmail.comFaculty of Environmental and Mining Engineering, Universidade Federal do Pará, Marabá, Brazil, Graduating of Faculty of Environmental and Mining Engineering, Bruno_rp_35@hotmail.comFaculty of Environmental and Mining Engineering, Universidade Federal do Pará, Marabá, Brazil, Graduating of Enviromental and Mining Engineering, ailtonpantoja@live.com

Reginaldo S. De PaivaFaculty of Environmental and Mining Engineering, Universidade Federal do Pará, Marabá, Brazil, Professor at Faculty of Environmental and Mining Engineering, regisabo@ufpa.br

ABSTRACTThe Sossego Mine at Canaã dos Carajás, state of Para, has about 60% of oxide copper and due to its low grade and the difficulties of the flotation process it is considered as an exploration waste. The heap leaching is currently considered the most efficient method to extract the copper from low grade ore. The main advantage of this process is its low capital and operating cost. To achieve an efficient heap leaching process, however, creating a porous heap with high permeability is essential. The ore small particles affect the heap permeability, prevent the efficient distribution of the leach solution and because of this, the metal recovery is low. This problem may be mitigated trough the agglomeration of the fine particles. In this study, to determine the conditions where the agglomerate achieves the best quality at the lowest cost, drum agglomeration studies were performed at a laboratory scale with the oxide copper fine particles, using sulfuric acid as binder agent. In this study, the relation between acid and water at the agglomeration process, the ore total moisture and the influence of the speed rotation were analyzed. To evaluate the agglomerate that was formed visual aspect, granule size distribution, resistance and integrity tests were studied.

INTRODUÇÃO

The oxidized copper makes up about 60% of the deposits of the Mine of Sossego- Canaã do Carajás/PA- and because its low level and difficulty processing by flotation is considered residue exploitation. The heap leaching is currently considered the most efficacious route of processing for extracting copper from low content ores, the main advantage of this process the low capital cost and operation.

The hydrometallurgical route allows treating ores by leaching with low levels, and compared to pyrometallurgical has the advantage of requiring little investment, have low operating costs and be more sustainable features, it reduces environmental impacts from discharges of SO2 in the atmosphere and allows recirculation of the reactants reducing the production of effluent (Paiva et al 2011).

Therefore, it is done to the agglomeration of fine ore prior to pile construction that offers several benefits, such as increased permeability, rapid and uniform flow of leaching solution through the stack, increasing metal recovery, shorter leach cycle and consequently, increased productivity and lower cost per ton (Kodali et al, 2011).

The agglomeration drum allows for consolidation of fine solid particles into larger granules using a binding agent and moderate shear. The solution of sulfuric acid is the most widely used binders in the agglomeration of oxidized copper ore and what is most cost effective. Subsequently the agglomerated, as is conventionally called the fines that pass through the agglomeration process is taken to leach column test simulating what occurs in cells.

The influence of rotational speed, of the total moisture in the ore and the acid / water ratio in the agglomeration process was analyzed. To evaluate the quality of agglomerates formed, beyond the visual aspect, particle size distribution, strength and integrity tests were done. In addition to results prepared at a laboratory scale, in order to obtain physical parameters present in the leaching process column. Simulating the heap leaching, using oxidized copper Sossego of Canaan Pa-mine and entered into a proposed mathematical model to predict the optimal height of the fluid in the column.

METHODOLOGY

The sample was oxidized copper from the Sossego’s Mine, locate in Canaã dos Carajás, Southeast of Pará. The sample was crushed, sieved, homogenized and divided by four to separate aliquots of 1.6 kg of ore. The size fraction used in the tests was below 5 mm, being 7.56% passes in 200 # (<75μm). The density and water content of the sample are, respectively, 2.573% and 2.58 g/cm3.

Trial testing: Agglomeration of Thin

The tests were conducted in a plastic drum laboratory scale (28 cm diameter and 27 cm high) with variable speeds in a windmill pitchers. Feeding ore and sintering time 30 minutes did constant. A suitable rotation speed of the agglomeration was determined by analyzing the behavior of the ore inside the drum at various speeds from 10 to 30rpm. To evaluate the influence of the water / acid and total moisture in the process, several tests were performed. The results that stood out for their results with the following parameters:

Test 10: 17.5% H2SO4 and 12.5% of water; Test 11: 16% H2SO4 and 13.5% of water; Test 12: 16% to 11% water H2SO4e; Test 13: 17.5% H2SO4 and 11% water.

Considering the humidity of the sample, 2.58% wet basis, was sprayed water on the ore to adjust humidity. Then, the mixed acid directly into the drum in rotation, the acid through a pipe equally distributed throughout the length, improving the homogenization. The mounting of the drum agglomeration is shown in Figure 1.

Figure 1 drum agglomeration.

Particle Size Analysis, Integrity and Strength of Particleboard

The particle size analysis was done of the agglomerates in each test series of the following sieves: 4, 8, 12 and Tyler Series 28 # / Mesh, for comparison purposes the particle size of the product to the particle size of the feed.

The method for determining the integrity of the agglomerated is to submerge it in a liquid solution and record the time and the behavior of its total disintegration. As Nosrati et al. (2011), the time it takes for the pellet to disintegrate gives an indication of the strength of re- humidify.

The compressive strength of the agglomerates was measured by determining the limit of resistance to compression. The test consisted of applying a compressive load in one direction on the agglomerated.

Preliminary tests Column: Flow Test

The flow test was performed with the aid of a peristaltic metering pump. With the previously prepared filter layer and filled with ore column, it takes the same to a stand where he was seated and properly positioned for receiving the fluid.

At the trial, there was the time that the liquid came into contact with the sample, then brokered the flow rate output and when the liquid reaches the height of the column. The column was identified with those heights from the filter layer. Figure 2 illustrates the metering pump and identification for control flow.

Figure 2 Column used in flow control

Sets, the metering pump, the input flow in the liquid column to stabilize the height of 20cm. This control is important to prevent any overflow of the fluid, particularly with the use of acid solution.

Results and Discussion

Análise Granulométrica, Integridade e Resistência do Aglomerado

The results of particle size analysis of the feed and product agglomeration of the assays are shown in Figure 3. From these results we can see that in all trials particles smaller than 1.8 mm were all lumped.

The analysis confirms what was found in the visual assessment: The test 11 had the best result and the test 13 was the least efficient.

Figure 3: Curve of particle size analysis of food and crowding.

The result of the compressive strength and integrity of the pellets are shown in Tables 1 and 2, respectively. The compressive strength results show that the test pellets 11 had the best results with 91.90 kPa. In integrity test agglomerateds the test 10 had the best result and the disintegration time was 64 min.

Table 1 Compressive Strength of Agglomerates Formed in Each Test.

Test % of H2SO4

% of água

Compression strength of the agglomerated

(kPa)

Time of total disintegratio

n

12 16% 11% 59,22 39 min

11 16% 13,50% 91,9 58,4 min

13 17,50% 11% 50,29 39 min

10 17,50%

12,50% 44,04 64 min

Tests for compressive strength and integrity are important to predict the behavior of the agglomerated in the heap leach. These tests give an idea of the pressure the crowded stand in a pile and leaching time as he would begin to fall apart. Interestingly, the pellet is dissolved easily, the permeability of the cell will be compromised, which is totally the opposite of the function of the agglomeration.

Leaching test with crushed ore and agglomerated

Agglomerate

Tests using only the agglomerated of fine particles showed very low values in the output flow, close to zero, causing problems in the control of fluid flow, see Table 3.

Table 3 Results of the agglomerated flow oreFLOW IN COLUMN VALUE (L/H)Flow of initial entry 4,2 L/HFlow initial output 0,5 L/HFlow final entry 0,1 L/HFlow of final output 0,027 L/H

The value of 0,027 L / H flow in the final output is justified by the low time integrity of the material to break up caused the rapid decrease in porosity and clogging the filter layer by fine particles. Also difficult to control the stabilization of the net 20 cm in height, as can be seen in figure 6 below.

Figure 6 Relationship between the H2O level height in the column with the time - Particleboard

Figure 6 shows that at the time of 63 minutes approximately 1 hour at output flow showed almost constant at 0.027 L / H.

Below in Figure 7 one can see variations in flow rates of entry and exit controlled in an attempt to find the flow that will stabilize the liquid at the ideal height.

Figura 7 Controle de Vazão – aglomerado

Crushed with agglomerated

This mixture of crushed material to the agglomerated, the flow test, showed good results, both in control and in the flow of final output. The results of the flow are shown in table 4.

Table 4 Results of sample flow (50% crushed +50% agglomerate)FLOW IN COLUMN VALUE (L/H)Flow of initial entry 5,1Flow initial output 0,8

Flow final entry 1,68Flow of final output 1,7

Inicialmento the output flow presented below the input flow due to the creation of preferential flow for fluid flow values, but in the time of 231 minutes about 4 hours the liquid stabilized in the bed height of the sample at a rate of 1.7 U / H. The variation of the rise of liquid in the column until it stabilizes can be seen in Figure 8

Figure 8 The relationship between the height level in the column with H2O time - 50% crushed + 50% agglomerated.

In the graph above it appears that the liquid, after adjusting the fluid level has decreased, this is due to the excessive rise in porosity with reduced fragmentation of the agglomerate material. After 150 minutes Manteu liquid level constant at 20 cm height.

The changes in control flow previously said can be seen in Figure 9. In this it appears that the output flow reached a peak of 2.65 L / H for an input flow of 2.04 L / H, but the balanced flow in a flow rate of 1.7 L / H.

Figure 9 Flow Control of the sample (50% crushed + 50% agglomerated)

This flow of 1.7 L / H, which is an intermediate flow in the other two tests, shows that the mixture of crushed material with the agglomerated material can bring good results in the leaching process in cells, because the problems addressed in the test with crushed, as the non-use of fines and time of leaching liquid residence can be mitigated or solved using the two samples together.

Proposed Model

The control of the liquid level height in the column as a function of time was obtained with the experimental data and the observation equation of the physical parameters of inverse Laplace transform method. A model was generated to estimate the height of the liquid layer in function of time (equation 1).

H(t) = (equation 1)

Estimates of the Constants

The constants in the equation (1) were obtained by nonlinear regression method using the data obtained experimentally in the column. Being, Particleboard (Test 2) and crushed with Particleboard the rate of 50% (Test 3).

Answer Theoretical and Experimental

The figures 10 and 11 shows the comparison between the theoretical curves obtained with the equation (1) obtained in practice and the tests with the crushed and agglomerated ore.

Figure 10 Practical and theoretical curve after curve fit (test 2).

Figure 11 Practical and theoretical curve after curve fit (test 3).

The theoretical curve fits the experimental curve showing possible to control the height of the liquid layer in the leaching column.

CONCLUSION

Is it possible to perform clustering of copper ores in plastic drums, including on its interior surface, rails in straight lines in the direction transverse to the movement of the drum to cause the "snowball effect" and have controlled as a function of the height of the diameters rails. There is an optimized linear distance between these rails. To drum 28cm in diameter, two tracks of linear distance of about 45cm was the best that formed clusters.

The observations showed that below 14.6 rpm speed of rotation causes the effect of "slip particles", so without the formation of agglomerates. Since the above 18 rpm was verified the "cascade" effect, and therefore, the breakdown of the agglomerates were present. The speed of rotation that is best suited to testing was 17.5 rpm, yielding more balanced clusters of dimensions.

Tests for compressive strength and physical integrity executed with clusters showed that the test 11 showed the best performance because of agglomeration in order to view leaching in fixed beds, ie in columns or cells, a cluster with greater resistance to both compression and physical integrity, implies a better extraction efficiency.

Equation 1, shown to be a possible tool to control the fluid height in the leaching column, enabling predictions regarding the time required for half saturation occurs.

During the leaching process it is necessary to make specific adjustments to the input flow to avoid overflow. This is a measure of control in order to reach equilibrium, this occurs when the flow of output approaches the input value.

BIBLIOGRAFIA

A. NOSRATI, J. ADDAI-MENSAH, D. J. ROBINSON, J. FARROW. INVESTIGATION OF THE FUNDAMENTALS OF NICKEL LATERITE ORE AGGLOMERATION PROCESS. Disponível em: <WWW.CONFERENCE.NET.AU/CHEMECA2011/PAPERS/064.PDF >. Acesso em: 20 jan. 2014.

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