One of the Iranian copper deposits that is located east of Iran and also known as a primeval one in that area is Mesgaran Field. Old mining works have been clearly seen in the area. Iran is located on global copper belt and as a result it has numerous potential areas as copper deposits. The purpose of this study is identifying possible potentialities of copper mining in less developed regions of Iran with basic modern technologies. In this study, laboratory investigations of this field were done on samples via leaching and the cementation method. According to the study purposes, acid concentration, temperature, time and pulp density were selected as the main factors that were tested in leaching studies. Moreover, pH, temperature, time and the amount of iron powder were factors which were tested for copper cementation. Optimum conditions of leaching studies with 99.11% recovery rate were obtained after 120 grams per liter of H 2SO 4, 80 degrees Celsius, 2 hours and 100 grams per liter of solid to liquid. On the other hand, optimum conditions of cementation by iron powder were resulted at more than 95% with a pH of 3, 45 degrees Celsius, 1 hour and 1.5 times more than the stoichiometric equation of required iron powder amount to precipitate copper.
Mineral processing studies begin from initial exploration stage. As in the exploration using the geostatistics and the detection of the anomalous elements of the economic mineralization in the region [
Nowadays, sulfide minerals are not as pure as 50 years ago to smelt directly in a flash furnace and as a result, these low grade raw materials (less than 1% Copper included) should be processed by the flotation method to reach to an acceptable grade (more than 22% Copper included). After this step, matte smelting, matte converting and refining are applied to the product of the flotation step to obtain copper with more than 99% purity [
Oxide minerals as described formerly can be treated by the hydrometallurgy method that contains three main steps 1) Leaching, 2) Solvent Extraction (SX) and 3) Electrowinning (EW) [
Sulfuric Acid (H2SO4) is the most common chemical reagent that is used for the leaching of oxide minerals including copper ones [
The principle of cementation is based on electrochemical differences between ions capacity. Lead, Iron, Zinc and Aluminum are respectively the best metals that can recover copper from PLS [
This technical note is to report and document initial experimental findings that could lead to a new understanding of the role of Sulfuric Acid in the recovery of copper from oxide minerals.
Mesgaran Copper Field is located 29 km south of Sarbisheh City, east of Iran. Accessibility to the field is possible via Nehbandan-Sarbisheh Road. There is no rough topographic area in the field and nearly all of the field is accessible by usual cars. The geological structure of the area contains of mafic and ultramafic rocks. This field is a part of the Gold zone of Ahangaran-Bandan metallogenic province (
In Mesgaran mining area Copper mineralization has occurred in pillow-lava and andesite-basalt sequences of eastern Iran (
These veins cross out the volcanic complex as stockworks which include Chalcopyrite, Bournite and Pyrite. In this region, we observed no evidence proving massive deposit or lens shape deposit creation. The main observed minerals
are sulfide and oxide forms of copper. Malachite, Azurite and lower amounts of Tenorite and native copper in oxide supergene zone and chalcopyrite and bournite as the primary sulfides have been detected. Oxidation and erosion caused geotite and hematite around sulfide minerals like Chalcopyrite and Pyrite (
In this region, argillic alteration (presence of Montmorillonite mineral) as a secondary alteration process is observed too. Most of the copper is in oxide form on the surface and because of high degree of oxidation and erosion, sulfide mineralization is rare in outcrops so deeper samples are needed to study the deposit. Drilling is the best choice in such situations. According to mineralization and the host rock (pillow lava and andesite-basalt), the mineralization type seems to be categorized as a massive sulfide and redbed type. Generally the mineralization manner (copper mineralization as stockworks), the host rock (pillow lava and andesite-basalt), the deposit development environment (a volcanic part of an
Ophiolite sequence) and the alterations (quartz-carbonate, epidote and chlorite) observed in this region and comparing them to the massive sulfide types leads to classify Mesgaran deposit as a Volcanic Massive Sulfide (VMS) type. But still more studies are needed to prove this claim with higher accuracy [
200 kg of the sample is taken from Mesgaran Field after excavation. Then the sample is crushed by a jaw crusher and milled to obtain minus 120 microns size. After milling, XRF and XRD are applied to the sample to study phases and chemical composition. All tests and devices took place in laboratories of Amirkabir University of Technology. The main copper mineral phase in the sample is malachite and the main mineral phase of the sample is quartz that does not react with sulfuric acid. XRF device was X’Unique II Philips (
For leaching tests, sulfuric acid of Merck Company is selected and distilled water is used for dilution. Moreover, a hotplate and 250 ml beaker are used for these tests. The hotplate has a digital temperature regulator and magnetic stirrer. First,
the solution is prepared for each test in a beaker together with specified pH and after reaching a defined temperature, a certain amount of copper ore with a size fraction of minus 120 micron is added to the solution for doing leaching tests in certain time periods. Four factors of acid concentrations, temperature, time and pulp density has been studied in three levels by the Taguchi method. As a consequence, L9 Taguchi orthogonal array has been selected for leaching tests. Tests are designed with the Taguchi method and Variance analysis (ANOVA) has been done in Design Expert for leaching tests and Microsoft Excel for cementation tests. The value of each parameter at every level has been presented in
The cementation process of copper by iron powder is provided by following equation:
Cu 2 + + Fe ⇒ Cu + Fe 2 +
As a result of the differences in electrochemical potentials, a reaction will take place. The reaction potential of Iron and Copper is presented in
(∆G˚)298= −20.29 − 15.54 = −35.83 Kcal
According to the Gibbs free energy equation, the reaction will be obtained
Compound | Quantity% | Compound | Quantity% |
---|---|---|---|
SiO2 | 53.8 | Cu2O | 3.2 |
Fe2O3 | 21.5 | MnO | 0.4 |
Al2O3 | 10.9 | SO3 | 0.7 |
MgO | 5.5 | P2O5 | 0.5 |
CaO | 3.4 | Total | 100 |
Parameter | Level | ||
---|---|---|---|
1 | 2 | 3 | |
Acid concentration (gr/l) | 40 | 80 | 120 |
Time (minute) | 60 | 90 | 120 |
Temperature (Celsius) | 40 | 60 | 80 |
Pulp density (gr/l) | 100 | 150 | 200 |
Half Reaction | Standard reduction potential (E˚) | Gibbs free energy (∆G˚) |
---|---|---|
Cu2+ + 2e => Cu | −0.337 | 15.54 |
Fe2+ + 2e => Fe | 0.44 | −20.29 |
spontaneously. In order to perform cementation tests, 100 ml of copper ore was dissolved in the solution and added up to a 250 ml beaker, and after regulating pH, the temperature will be adjusted by the hotplate. After these steps, iron powder will be added up to the solution in order to study the test.
In order to study the cementation of copper by iron powder, four parameters of pH, temperature, time and amount of iron powder were optimized in three levels by the Taguchi method. The value of each parameter at every level has been presented in
The technique of defining and investigating all the possible conditions in an experiment involving multiple factors is known as the design of experiments. Basically, classical parameter design, developed by Fisher, is complicated and not easy to use. Especially, a large number of experiments must be conducted when the number of the process parameters increases. To solve this problem, Taguchi method uses a special design of orthogonal arrays to study the entire parameter space with a small number of experiments only [
Experimental designs were first introduced by Fisher as an agricultural research tool in the 1920s [
Parameter | Level | ||
---|---|---|---|
1 | 2 | 3 | |
pH | 0 | 1.5 | 3 |
Temperature (Celsius) | 25 | 35 | 45 |
Time (hour) | 0.5 | 1 | 1.5 |
Iron powder (stoichiometric amount) | 1 | 1.5 | 2 |
characteristic was a major advantage of the technique but a major disadvantage of one-at-a-time variable testing. Main effects and interactions could be confounded, with one another if the experimental design of low resolution were chosen [
The L9 array leaching tests which are modeled by the Taguchi method are inserted in
After 9 tests with the Taguchi method, 1 factor diagrams of acid concentration to recovery rate was obtained as shown in
According to
According to chemistry principles, an increase in temperature will result in a progress of elements motion which means it will lead to more reactivity of complex. Based on our test results which can be seen in
Similar to most leaching tests, increasing the pulp density will cause a decrease
No. | Acid concentration (gr/l) | Time (minute) | Temperature (Celsius) | Pulp density (gr/l) | Cu recovery (%) |
---|---|---|---|---|---|
1 | 40 | 60 | 40 | 100 | 82.74 |
2 | 40 | 90 | 60 | 150 | 62.67 |
3 | 40 | 120 | 80 | 200 | 78.75 |
4 | 80 | 60 | 60 | 200 | 86.96 |
5 | 80 | 90 | 80 | 100 | 92.44 |
6 | 80 | 120 | 40 | 150 | 77.75 |
7 | 120 | 60 | 80 | 150 | 84.10 |
8 | 120 | 90 | 40 | 200 | 81.02 |
9 | 120 | 120 | 60 | 100 | 99.11 |
in recovery rate, where in some tests it has been seen that after a maximum level for pulp density, reactions will come to an end. In this case, the anomaly point has occurred where it is expected to further decrease the recovery rate. Incidentally, the lower level in pulp density will result in a greater recovery rate (
According to the obtained models in the software, factor interactions have been investigated to gain better cognition of the process and increase the efficiency of operation. For this purpose, interaction of temperature and pulp density are depicted in
decreasing pulp density results in a greater recovery rate of the operation, while time played a twofold role in this diagram. In addition, interaction of time and temperature as shown in
Interaction of acid concentration and time is shown in
According to the obtained diagram in
lead to substitution of Copper ions with Iron ions in solution.
With a more detailed look at
As it has been seen in
The last parameter which is examined in the tests was the total amount of iron powder that is needed for the reaction. Due to test results, increasing the amount of iron powder that is measured by stoichiometric quantities, tends to increase the copper recovery rate of the cementation process (
Mesgaran copper field which is also known as one of the primeval mines in east of Iran, was examined with numerous tests to be run as a modern mine with new technologies. As it has been observed, the economic mineral in this field is
malachite which is encompassed by quartz gangues that leads the experiments to leaching tests with H2SO4 instead of flotation or physical separation methods. Hence, after taking samples from the field, the test was designed via the Taguchi and Variance analysis method. Afterward, tests were performed in the Amirkabir University of Technology laboratory to gain optimum conditions of leaching and cementation operation. In the leaching operation, four factors of acid concentration, temperature, time and pulp density have been studied at three levels. Moreover, in order to study copper cementation by iron powder, four factors of pH, temperature, time and amount of iron powder, are optimized at three levels.
Finally, it is found that increasing acid concentration, temperature and time will cause an increase in the copper recovery of ores with the leaching method. On the other hand, increasing pulp density will have a reverse reaction. From another stance, in the cementation process, the recovery rate of copper increased by maximization of pH, temperature and a lower rise in time and iron powder amount. Optimum conditions of leaching studies with 99.11% recovery rate came after 120 gram per liter of H2SO4, 80 degrees Celsius, 2 hours and 100 gram per liter of solid to liquid. In addition, the optimum conditions of parameters during the cementation process with iron powder were obtained at more than 95% with a pH of 3, 45 degrees Celsius, 1 hour and 1.5 times more than the stoichiometric amount of copper.
Technical and data supports from Amirkabir University of Technology (Tehran Polytechnic), Prof. Ardeshir Hezarkhani and Tehranpadir Co. are acknowledged.
The authors declare no conflicts of interest regarding the publication of this paper.
Khakmardan, S., Shirazi, A., Shirazy, A., Hosseingholi, H. (2018) Copper Oxide Ore Leaching Ability and Cementation Behavior, Mesgaran Deposit in IRAN. Open Journal of Geology, 8, 841-858. https://doi.org/10.4236/ojg.2018.89049