Research on New Technology of Diamond Purification

About the Author:

Zhang Ge, Gao Gong, graduated from the Department of Nonferrous Metallurgy of Northeastern University. He has worked in electrolytic aluminum, electrolytic magnesium, electrolytic copper powder, nickel powder and lead powder. In 2005, he entered the diamond synthesis industry and worked on the research of synthetic diamond raw materials.

【 Abstract】 This paper proposes a new flow chart of diamond purification process through the analysis of the drawbacks of the current mainstream process of diamond purification, and demonstrates its rationality. It is confirmed that this technology will replace the current process in a short period of time, achieving the goal of saving energy and resources, reducing costs and improving the environment. The new process can increase the efficiency by three times, and the electricity saving per ton of metal is 3000-4000KWh.

I. Introduction

Now the diamond industry has ushered in the opportunity of great development, but the diamond purification process is a "tumor" that restricts the development of the enterprise. It must be treated as a large-scale operation to get medical treatment and get a new life.

At the heart of the current diamond purification process is the technique of separating the metal catalyst from graphite and diamond by "electrolytic synthesis blocks." The technology is to crush the synthetic column into a certain particle size (without destroying the diamond crystal grain) into the anode bag for electrolysis, the electrolyte dissolves the metal in the synthesis block into metal ions, enters the electrolyte, and then discharges on the cathode plate. After reduction to metal, the remaining graphite and diamond are ball milled (or pressed), sieved, about 10% of the sieve material is returned to the secondary electrolysis, and the sieve is sent to the shaker for sorting to separate the diamond from the graphite. . This process is immature and unreasonable, so that it has many drawbacks. It has become a "tumor" in the enterprise, causing great pollution and harm to the environment. It is time for non-complete remediation.

Second, the main problems of the current diamond purification process

The core technology of the current process is "electrolysis of synthetic blocks" which is a soluble anode electrolysis. The main problem with this process is the choice of recycling the metal by means of an "electrolytic synthesis block". This is a fundamentally wrong choice. The synthetic block is placed in the bag together with the anode plate and suspended in the electrolytic cell. It is stationary, and the material and the anode plate in the bag are also compacted without being pressed. The metal catalyst is slowly entered into the bag by the electrolyte, penetrates into the synthesis block and undergoes oxidation reaction with the exposed metal surface, so that the metal enters the electrolyte in the form of Fe ²⁺ , Ni ²⁺ , Co ^{2+ ,} and the like. For the block after high temperature and high pressure, the electrolyte is difficult to dissolve the metal quickly. It usually takes 5-8 days. How much energy does it consume and how much material is wasted in such a long time? How much pollution is caused to the environment? Therefore, diamond synthesis companies generally hide this part in a remote corner, which is not easy to be noticed.

It is understandable to choose an electrolytic process to recover metal. If a good process is placed in an extremely unreasonable position, it will not work. Here are two examples similar to the "electrolytic composite block". For comparison, it is not difficult to find out whether this choice is reasonable or not.

(1) In terms of copper electrolysis scouring: blister copper or copper alloy is cast into an anode plate, electrolysis is carried out in an electrolytic cell, and refined copper is obtained on the cathode plate, and its direct current consumption is only 230-280 KWh/ton of copper.

(2) In the copper slurry electrolysis: firstly grind the chalcopyrite to 10-65μm, then put it into the anode bag for electrolysis, and obtain the copper powder at the cathode. The DC power consumption is only 1000-1500KWh/ton of copper powder. It is intended that the pulp is electrolytically treated with chalcopyrite (sulfurized ore) rather than pure metal, and the difficulty is conceivable.

Associating with the "electrolytic composite block", the metal is a highly dispersed particle, which is wrapped in layers, and can not be ground very fine, but also into the bag, which belongs to the "diaphragm electrolysis" application in this process, so that the overall voltage of the anode It is more than 70% of the tank voltage, so choosing the "electrolytic composite block" is in a disadvantage in three key aspects, which is an extremely unreasonable choice.

In summary, the main problems in the current diamond purification process are:

1, the electrolysis cycle is long, generally 5-8 days, the general synthetic diamond from the mixing to the press synthesis takes only two days, and the process is so long, can not be said to be a waste of time, time is money Yeah!

2, the power consumption is too high, because the current efficiency is low, only 53-65%, the tank voltage is too high, resulting in excessive power consumption, the general DC power consumption is 6000-9000KWh / ton of metal, is a high-energy project.

3, wasting a lot of raw materials, the unit price of the electrolyte is 10,000 yuan / ton, other materials are also very expensive, increasing the manufacturing cost of diamond

4. Some enterprises are unreasonable in the selection of electrolytic equipment, which brings many difficulties to the normal operation of the equipment.

5. The discharge of the three wastes is not up to standard, which seriously pollutes the environment and damages the health of the operators and surrounding residents.

In view of the above problems, we cannot help but say that this is a backward process technology that should be eliminated.

Third, the new diamond purification process flow chart

The current diamond purification process has many drawbacks. The fundamental reason is that the selected process is unreasonable and the selected equipment is not reasonable. The diamond synthesis process is a very young professional. It needs to learn from other professions and other professional technologies. The electrolysis process is a pure electrochemical process, which is still very strange to people in the industry. The process is a mature technology often used in the chemical industry and the metallurgical industry. There are many kinds of processes, depending on whether you can choose the right one or not.

This paper proposes a new process, mainly to solve the speed problem of chemical reaction or electrochemical reaction, so that it is more in line with the requirements of chemical reaction kinetics. The new diamond purification process flow chart is shown in the figure below.

Diamond purification process flow chart

Fourth, the rationality of the new diamond purification process

1. Select the reaction kettle as the metal dissolution equipment. This is the best choice.

The reactor is one of the most mature equipments for chemical production. It is an effective means to crack graphite-catalyst. Large reactors can hold several tons of materials at a time. The kettle has electric heaters, which can be used to control the optimum reaction temperature. The mechanical agitator can continuously rub the friction between the synthetic block and the acid in the kettle, and continuously expose the new reaction interface. At the same time, H2SO4 and HNO3 can also acidify the graphite to form expandable graphite, which makes the graphite expand and refine. , expose the metal. Since the reactor can be temperature-controlled, it can be stirred, and it can be pressurized at 0.1-1.0 MPa to increase the reaction rate, which are all necessary conditions for chemical reaction kinetics.

In daily work, it is often encountered to deal with diamond synthesis samples, that is, the sample is properly broken, and then soaked with H2SO4, HNO3 mixture, the diamond can be separated in 1-2 hours, but the current purification process takes 5-8 days. Time is really incredible.

It takes only 10-15 hours to leaching the metal in the reactor (the loading can be about 1-3 tons). It can be seen that the reactor is a high-efficiency reaction vessel, which can fully meet the requirements of the process.

2. The new process selects the aqueous solution electrolysis process in hydrometallurgy, which is the most mature electrochemical extraction metallurgy technology in non-ferrous metallurgy. Its current efficiency can reach over 98%, DC power consumption is 3000-4000KWh/ton metal, one electrolysis cycle It takes only 24 hours to complete, and the depleted electrolyte is simply processed and returned to the reactor for the next round of leaching, thereby achieving rapid electrolysis and saving energy.

3. High metal recovery rate

The first point to ensure high recovery rate is that the metal is well leached. The second point is that aqueous solution electrolysis is one of the strongest oxidation-reduction processes. The electrode potential of Ni and Co is known from the electrochemical electrode potential sequence of the element.

Electrochemical data of catalyst elements

Both are positive than Fe, so it is preferred to reduce the deposition on the cathode plate, which ensures the recovery of valuable metals.

Therefore, the new process selects the reaction vessel to dissolve the metal, and selects the aqueous solution to extract the metal. This is a strong combination. This is the two highlights of the new process. It is an industrial design that guarantees a multi-, fast, good, provincial and environmentally friendly product.

V. Conclusion:

The current diamond purification process has completed its historical mission and can no longer meet the needs of current economic and social development. We should change the way of economic development, keep pace with the times, innovate constantly, and vigorously promote the promotion and application of new technologies.

The new process flow chart is a scientific and reasonable combination, which not only can bring economic benefits and environmental benefits to the enterprise, but more importantly, it changes the weakest link in the enterprise and enables the enterprise to economize resources and save energy. An environmentally friendly and sustainable health path.

Due to the limitation of space, this article cannot explain the technical conditions and operation techniques of each link in the process. It will be imparted to the project unit in the chemical and electrochemical engineering training of operators and technicians in the future project implementation process.

Industry experts, industry colleagues criticized and corrected.

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