In this study, the leaching and adsorption circuits of the plant, which were calibrated in the previous section, are simulated and the effect of the carbon transfer strategy in the adsorption section is analyzed. The study of the activated carbon transfer strategies in the CIL and CIP processes is a practical problem of interest for both the design and the operation of gold extraction plants Carrier et al.
The use of simulators to analyze this problem is very useful because experiments in pilot plants are expensive and complex. Some results are available from previous studies using other minerals and operational conditions Stange, In the present study, other strategies not addressed yet are taken into account and the simulated flow rate and concentrations are used to calculate the performance indices to be used for a systematic comparison between the strategies, which helps identifing the carbon transfer strategies most relevant to this process.
The evaluation of the carbon transfer strategies uses the following metallurgical performance indices:. Subscript "1" stands for inside the first tank and "7", for the exit of the last tank. The following strategies of sequential transfer of carbon in the adsorption circuit are simulated for 37 hours and then the metallurgical performance indices are calculated and analyzed:.
After five hours of rest without carbon transfer , the loaded activated carbon is transferred from the first tank to the elution process for one hour, and after another hour of rest the activated carbon is transferred from the second tank to the first. This procedure is repeated for the other tanks until new activated carbon is added in the seventh tank. After one hour of rest the transfer cycle is repeated. After five hours of rest new activated carbon is added to the seventh tank during one hour, after another hour of rest the activated carbon is transferred from the seventh to the sixth tank, and after an additional hour of rest the activated carbon is transferred from the sixth to the fifth tank.
This procedure is repeated for the other tanks until the loaded activated carbon has been transferred from the first tank to the elution process. After five hours of rest the activated carbon is transferred from the sixth to the fifth tank, after another hour of rest the activated carbon is transferred from the seventh to the sixth tank, after an additional hour of rest new activated carbon is added to the seventh tank during one hour, and then after another hour of rest the activated carbon is transferred from the fifth tank to the fourth.
This strategy is similar to strategy 2 except that the activated carbon transfer from the sixth to the fifth tank, the fifth to the fourth tank, the fourth to the third tank, and the third to the second tank is synchronized. This strategy is similar to strategies 2, 4, and 5 except that the addition of new activated carbon in the seventh tank and the transfer of the seventh to the sixth tank, the sixth to the fifth tank, the fifth to the fourth tank, the fourth to the third tank, and the third to the second tank are synchronized.
This strategy is similar to strategies 2, 4, 5, and 6 except that the addition of new activated carbon in the seventh tank and the transfer of the seventh to the sixth tank, the sixth to the fifth tank, the fifth to the fourth tank, the fourth to the third tank, the third to the second tank, and the second to the first tank are synchronized. This strategy is similar to strategies 2, 4, 5, 6, and 7 except for addition of new activated carbon in the seventh tank and synchronization of all the transfer pumps.
After five hours of rest the activated carbon is transferred from the fifth to the fourth tank, after another hour of rest the activated carbon is transferred from the sixth to the fifth tank, after an additional hour of rest the activated carbon is transferred from the seventh to the sixth tank, then after another hour of rest new activated carbon is added to the seventh tank during one hour, and after one more hour of rest the activated carbon is transferred from the fourth to the third tank.
The results of the metallurgical performance indices see Eqs. The results for the performance indices show that the total amount of gold fed into the circuit, the amount of cyanide lost at the exit of the circuit, and the amount of carbon added to the adsorption circuit are identical in all activated carbon transfer strategies.
Also, the amount of gold lost with the ore is virtually independent of strategy because the gold content of the ore is already very low in the adsorption section. Due the fact that the simulation results are not completely in a stable cyclic regime, which would be reached after a larger number of transfer cycles and a longer simulation time, the unbalanced gold mass indicates a continuous accumulation in the activated carbon.
This is assessed by the amount of gold accumulated in the circuit see Eq. In this case study the most important performance indices are the amount of gold recovered, the amount of gold lost in the liquid, and the amount of gold held in the circuit. By analyzing these indices one can observe that for strategy 1 the amount of gold recovered is very small, the amount of gold lost is very large, and a lot of gold is accumulated; on the other hand, for strategy 7 the amount of gold recovered is large, the amount of gold lost is small and less gold is accumulated than in strategy 1.
These results indicate that strategy 1 can not be recommended and strategy 2 and its variants are the best. Synchronization of carbon transfer pumps strategies 4, 5, 6, 7, and 8 may give better results than the sequential strategy when the amount of carbon loaded in the first tank is larger see strategies 2 and 4, 5 and 6 ; however, the performance of the process in the case where all pumps are transferring the carbon simultaneously strategy 8 is as bad as that of strategy 1 because the residence time of the carbon in the rich solution in the first tank is very small.
Finally, one can observe that strategy 6 is the most effective in decreasing the gold loss in the liquid phase and increasing gold recovery with values larger than those for strategies 1 and 2. Note that as one increases the mixing in the circuit by turning on the transfer pumps simultaneously strategies 4, 5, 6, 7, and 8 , the gold recovery reaches a maximum value for strategy 7 and thereafter decreases, while the loss of dissolved gold reaches a minimum value for strategy 6 and thereafter increases again.
A dynamic phenomenological model that describes gold leaching and adsorption on activated carbon is presented. This model can be easily simplified to represent the CIL, the CIP, or the leaching process and it can take into account more complex rate equations. In this study, the model was initially fitted to an experimental data set for the leaching section cascade of a plant and then for the adsorption section cascade CIL process of the same plant. The calibration results are good and describe well the plant dynamics; also the kinetic parameters found are in agreement with those presented in the literature.
The two sections of the plant were simulated together and several carbon transfer strategies were analyzed using as performance indicators, metallurgical indices. In spite of the fact that the simulated plant was not completely in a stable cyclic regime, the simulated results indicate that there are more appropriate strategies for enhancing the gold recovery in activated carbon and for reducing gold loss in the liquid phase, especially that in which an important amount of activated carbon is held in the first tank and the contact time between the carbon and the pulp is long.
Daniel Hodouin Laval University, Canada and Ann Bax Murdoch University, Australia are gratefully acknowledged for the useful discussions and for providing the experimental data used in this work. Abrir menu Brasil. Brazilian Journal of Chemical Engineering. Abrir menu. Adams, M. The chemical behaviour of cyanide in the extraction of gold. Kinetics of cyanide loss in the presence and absence of activated carbon, Journal of the South African Institute of Mining and Metallurgy, 90 2 , Bailey, P.
Stanley, G. Carrier, C. Salter, D. Wyslouzil, and G. McDonald, Pergamon Press, Coetzee, J. Counter-current vs co-current flow in carbon-in-pulp adsorption circuits, Minerals Engineering, 12 4 , Modeling, control, and optimization applied to the gold hydrometallurgy, Ph.
Thesis, Laval University, Canada. Comparison of empirical and phenomenological approaches to the analysis of gold cyanidation plant performance. In: Laplante, A. CIM Special Volume, no. A lumped kinetic model for gold cyanidation, Hydrometallurgy, 79 , Simulation study of the optimal distribution of cyanide in a gold leaching plant, Minerals Engineering, 19 13 , Dixon, S. The centrifugal force within the coupled fluid acts on the solids as they first enter the casing, transitioning the direction of the solid long before it can come into contact with the rotation impeller.
With the majority of the solid, in this case, carbon, never impacting the impeller, particle degradation is minimized. Furthermore, the acceleration of the product and its transition into the discharge pipe is smooth and gentle, again minimizing degradation. Be sure your motor HP is sufficient to cover run out and the high slurry density inherent to this type of application.
Our application engineers are well versed in carbon handling and are just a phone call away. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Leave a Reply Cancel reply Your email address will not be published. Thus we can separate solid-liquid separation tea aromas from tea leaves filtration for example. At this stage , we have been able to extract aromas of tea from the tea leaves by changing the physical shape of the tea aromas.
It is the same principle used in the leaching of gold. The gold that is in solid form in the ores turned into liquid form with cyanide in the presence of oxygen. The second step is the adsorption of gold on the surface of the activated carbon. Following a natural phenomenon known around the world positive charges attract negative charges Gold sticking to coal.
The solution from the hot wash is transferred to the electrolysis where pure gold is recovered. Carbon-in-pulp CIP is the sequential leach then absorption of gold from ore. During the CIP stage, pulp flows through several agitated tanks where sodium cyanide and oxygen have been added to dissolve gold into solution. In the absorption stage, this solution flows through several agitated tanks containing activated carbon. Gold absorbs onto the activated carbon, which flows countercurrent to the pulp, while screens separate the barren pulp from the gold-loaded carbon.
Carbon-in leach CIL is a simultaneous leach and absorption process. The simultaneous leach and absorption phases of the CIL process were developed for processing gold ores that contain preg-robbing materials such as natural absorptive carbon. These reduce the gold yield by attracting gold meant for the activated carbon. Simultaneous leaching and absorption help minimize the problem.
Process Description. A CIP circuit utilizes the same flowsheet as an agitated leach circuit up to the point where the slurry discharges from the final agitated leach tank. At this point, the precious metal values arc recovered directly from the slurry onto granulated activated carbon in agitated CIP tanks The carbon is retained in the tanks by any one of several different types of screens through which the slurry discharges CIP circuits are typically designed with at least four tanks to prevent short-circuiting of sluny and allow sufficient retention time for recovery of all the metals.
CIL circuits are similar to CIP circuits with the exception that leaching and extraction occur simultaneously in agitated leach tanks that also contain carbon and are equipped with carbon retention screens. The evaluation of agitated tank leaching verses CIP and CIL circuits is not as complex as the heap leach-agitated tank leach analysis. CIP and CIL circuits generally have lower capital and operating costs for gold ore bodies than agitated tank leach circuits.
Silver ore bodies show better economics with agitated tank leach-Merrill Crowe circuits. Counter-current leaching.
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