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Electro-oxidation of molybdenite decomposition process

Author: WenZhenQian
Tutor: ZhongHong
School: Central South University
Course: Chemical processes
Keywords: molybdenite the electrochemical reactor(ECR) electro-oxidation anode kinetics
CLC: TD954
Type: Master's thesis
Year: 2009
Downloads: 84
Quote: 0
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Executive Summary

Molybdenite from Jiangxi Dexing Copper Mine is reaserched. For disadvantages of common decomposing molybdenite technique, the good-prospect leaching technique without ejection was designed. It is hydrometallurgical process of electro-oxidation for Molybdenite.The trunk electrochemical reactor (ECR) was designed. And its operation mode is intermittent. The material of the cell body is made of polypropylene. The inert anode adopts DSA (dimension stable anode) with the coat consisting of RuO2 and TiO2, while cathode material uses the steel net with the low emitting hydrogen potential. Through experiment, the voltage of the electrolytic cell is calculated to be about 3.8V and the interelectrode distance is 10mm. The attended mode between each pair of electrodes is parallel connection. When at work, the electrolytic cell is put into stable temperature horizontal bath, add electric stir rods between electrodes, and put the probe of pH meter into pulp in order to keep the stable temperature of the additional electrolytic cell, strengthen mass transfer and control pH value.In the hydrometallurgical process of electro-oxidation for Molybdenite, Mo in molybdenite can be oxidized into negative ion MoO42-, which is soluble in electrolyte, by Cl2 generated in the process of NaCl solution electrolysis and HClO or NaClO transformed by Cl2. The best process condition in the research is that under room temperature, pH of the pulp in the reaction process is about 9, NaCl concentration in the electrolyte is 4.0mol/L,liquid-to-solid ratio of pulp is 25,the mixing speed is 400rpm, the current density of electrolytic cell is 466.0A·m-2 and cell voltage is 3.5 to 3.8V. Under this condition, 5 grams molybdenite can be completely decomposed in only 240 minutes, with leaching yield of molybdenum at 98 percent and current efficiency at 70 percent. In the process of electrolysis, there is neither Cl2 spilled out, nor metal deposited on the cathode.Anodizing curve kinetics shows that the oxidation leaching of molybdenite mostly depends on chlorine emitted by the anode. Mixing is helpful to diffuse the mass transfer, boost ion migration speed in the electrolyte, and make it easier for molybdenite granules to get to anode surface so that electric current increases. The increase in pulp concentration is bad for anodic chlorine generation, which will decrease electric current. Leaching process kinetics indicates that in the room temperature, when pH is 3, liquid-to-solid ratio is 25, mixing speed is 400rpm, and NaCl concentration is 4.0mol/L, the data processing we get is in accord with the kinetics equation of shrinking particle model. According to the data, leaching apparent activation energy is 8.282KJ/mol, and the process is mainly controlled by fluid diffusion. When pH is 9, liquid-to-solid ratio is 25, mixing speed is 400rpm, and NaCl concentration is 4.0mol/L in the room temperature, the data processing we get conforms to the kinetics model of solid reactant generated. Through calculation, the leaching apparent activation energy is 8.56kJ/mol, and there are solid reactants generated on the reaction interface. The whole process is controlled by liquid film diffusion.According to the process oxidation mechanism analysis,it is showed that the oxidant is HClO and Cl2 under the acidic condition,and the S element is oxidanted to SO42-; but under the alkaline condition ,the oxidant is NaClO and part of S element is oxidanted to sulfur. This didn’t affect leaching yield of molybdenum.

Full-text Catalog

Abstract     3-4
ABSTRACT     4-9
Preface     9-10
literature review     10-22
the nature and purpose of the 1.1 molybdenite     10-12
1.2 molybdenite decomposition process     12-19
1.2.1 roasting oxidation process     12-15
1.2.2 full wet decomposition process     15-19
the 1.3 electric oxidative reaction kinetics foundation     19-21
1.4 thesis thinking     21-22
second Chapter experiment Pharmacy, instruments and research methods     22-31
2.1 experimental raw     22-23
2.2 laboratory equipment     23-24
2.3 Reagents     24
2.4 electrolyte analysis     24-26
2.4.1 electrolyte free chlorine analysis     24-25
2.4.2 electrolyte sodium hypochlorite analysis     25
2.4.3 electrolyte sodium chlorate analysis     25-26
2.5 Mo analysis     26-29
2.6 Mo leaching rate and current efficiency calculation     29-31
2.6.1 Mo leaching rate calculation     29
2.6.2 current efficiency calculated     29-31
Chapter molybdenite electric oxidation reactor design     31-39
3.1 reactor tank design     31-33
3.1.1 reactor structure select     31-32
3.1.2 reactor work select     32
3.1.3 reactor tank material selection     32-33
electrode of 3.2 reactor design     33-38
3.2.1 electrode materials selection     33-34
3.2.2 electrode links select     34-35
3.2.3 cell voltage to determine     35-37
3.2.4 electrode spacing determine     37-38
3.3 Additional features designed     38
3.4 This chapter Summary     38-39
Chapter electro-oxidation of molybdenite decomposition process     39-51
4.1 electro-oxidation process operating methods and processes     39-40
4.2 electro-oxidation process factors studied     40-49
4.2.1 process pH Control electrolytic oxidation of molybdenite are found;   40-43
4.2.2 sodium chloride concentration of the electrolytic oxidation of molybdenite     43-45
4.2.3 liquid-solid ratio L / S of electrolytic oxidation of molybdenite     45-46
4.2.4 stirring speed electrolytic oxidation of molybdenite     46-47
4.2.5 current density electrolytic oxidation of molybdenite     47-48
4.2.6 detection characterization     48-49
4.3 This chapter Summary     49-51
electro-oxidation process mechanism in Chapter molybdenite explore     51-73
5.1 does not control the mechanism of pH process     51-53
5.1.1 electro-oxidation process pulp pH changes     51-52
5.1.2 electro-oxidation process mechanism analysis     52-53
5.2 DSA anode oxidation kinetics     53-56
5.2.1 electrolyte anode polarization curve     53-54
5.2.2 stirring speed anodized     54-55
5.2.3 pH anodized     55-56
5.2.4 liquid to solid ratio of anodic oxidation     56
5.3 cathode reaction mechanism analysis     56-58
5.4 electrical changes in the oxidative leaching process oxidants     58-59
5.4.1 electrolysis of sodium chloride oxidant changes     58-59
5.4.2 electro-oxidation pulp oxidant changes     59
5.5 electro-oxidation leaching process dynamics     59-68
5.5.1 leaching process dynamics model     59-63
5.5.2 leaching process dynamics research     63-68
5.6 of electrolysis process phase analysis     68-72
5.7 This chapter Summary     72-73
Chapter 6 Conclusions and Prospects     73-75
References     75-79
Acknowledgements     79-80
studied papers published by the Master of the period     80

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