Scientific journal

European Journal of Natural History

ISSN 2073-4972

ИФ РИНЦ = 0,301

Potassium permanganate has a reasonable industrial significance. Its facilitation is based upon oxidation characteristics; KMnO4 is used as a rective for permanganatometry, revealing dual links, synthesising glycols, oxides, aldehydes and ketones, saccharin. Potassium permanganate is also used for bleaching variuos materials, in processes of synthesising and analysing organic substances, colorants. It is known that it is facilitatated as an indicator of polymerization, in production of catalysts, air cleaning, pyrotechnics, antiseptic medications, oxidising «caps» of nanotubes [1–2].

Historically the first method of receiving potassium permangant [3] is synthesising potassium manganate (VI) from polianite and alkali in reaction with oxygen and baking on the air:

2MnO₂ + O₂ + 4KOH = 2K₂MnO₄ + 2H₂O. (1)

Then the received alloy is lixiviated with water, and transformation of manganate into permanganate takes place in the received alkali solution. Stage of transforming manganate into permanganate can include:

1. Boiling the solution – formation of potassium permanganate takes place as a result of disproportioning manganate (VI) according to equation of reaction:

3K₂MnO₄ + 2H₂O = 2KMnO₄ + MnO₂ + 4KOH. (2)

2. While processing СО2 solution the process of disproportioning accelerates, the reaction takes place according to equation:

3K₂MnO₄ + 2CO₂ = 2KMnO₄ + MnO₂ + 2K₂CO₃.  (3)

Due to formation of МnО2 the process is unfavourable and it is necessary to regenerate KOH from the formed potash according to the reaction:

K₂CO₃ + Сa(OH)₂ = 2KOH + СaCO₃↓. (4)

3. Oxidation of manganate with chlorine according to reaction:

2K₂MnO₄ + Cl₂ = 2KMnO₄ + 2KCl (5)

is also unfavourable due to losses in potassium as KCl, regenerating KOH form them via electrolysis requires a lot of resources. Therefore, electromechanical method of transforming manganate into permanganate is being developed.

Nowadays a technology of receiving potassium permanganate through a combined (two-stage) method is generally accepted [4]. Polianite is mixed with KOH abd exposed to alloying in baking pots at the first stage, the reaction takes place according to equation (1).

The received allow is lixiviated, and the received solution is exposed to electrolysis at the second stage. At the same time, ion MnO^-₄ is oxidized on anode:

MnO^2-₄ - е^- = MnO^-₄ (6)

and alkali and hydrogen are formed on katode:

2H₂O + 2е^- = H₂ + 2OH^-.

Final equation:

2K₂MnO₄ + 2H₂O = 2KMnO₄ + 2KOH + H₂. (7)

Crystals KМnО⁴, formed on electrolytic cell, are discharged, washed, and exposed to re-crystallization, and then dried and packed [3].

The described combined technology of receiving potassium permanganate has the following disadvantages: long duration of alkaline alloying, low output of potassium manganite, high energetic costs. Therefore, works on improving production process have been undergoing constantly, their objective is to decrease energy costs and increase product output.

One-stage technology of receiving potassium permanganate from manganese dioxide has been suggested by an author of American patent [5]. This technology consists of electromechanical oxidation of MnO2 suspension in solution of potassium hydroxide with implementation of katode in porous container and high concentration of alkali (10–25 mole/dm3) inside the container. The method has been suggested for regenerating permanaganate in alloying baths and is described by a great consumption of electric energy (14 kVt∙hr/kg) that exceeds energy consumption (0,7 kVt∙hr/kg) of the combined technology. The listed methods testify for a contimuous search in the studied area that is linked to developing methods that provide for a complete facilitation of raw material (transforming a greater part of initial materials into the product) and increase in product output.

Dozens of patents are known. One-stage tehcnologies are being developed. However, only one method is used in industry – electromechnical oxidation of potassium manganate (IV).

Disadvantages of the existing method of receving potassium permanganate:

1. Long duration of the process of alkaline manganate alloying. This stae continues for no less than 24 hours.

2. Insufficient output of potassium manganate (VI) suring the stage of alloying – no more than 60 %, and, therefore, greater consumption of raw materials.

3. The process of producing КМnО4 includes many operations with a powerful alkaline solution.

4. Potash is formed in case of continuous contact with air, and therefore, a necessity to regenerate alkali emerges. During caustification of potash with quicklime – CaO or slaked lime – Ca(OH)₂, consumption equals 0,7 t (in calculation to 100 % of CaO) per ton of permanganate.

5. High specific consumption of energy – 1383 kJoule/mole of permanganate. Therefore, development of methods that possess improved characteristics is reasonable [1].

The objective of this work is to receive permanganates of the existing impoverished ores, cheap carbonate ores that are commonly present in Russia, have been used for this purpose. As a result of numerous exams, we have defined liquid-phase process with facilitation of gaseous chlorus as an oxidant. In order to maintain nearly neutral pH of the solution, carbonate ore contains calcium carbonate that serves the purpose of buffer during liquid-phase chlorination of carbonate ore. Perfect conditions for chlorus hysrolysis with receipt of HCl and HOCl are created under temperature 40–80 °С. A weak hydrochloric acid interacts with CaCO3, and HOCl oxidates MnO2 to Ca(MnO4)2 in these conditions. The discharged CO2 provides of oxidation of one unstable manganese salt by another with a direct receipt of Ca(MnO4)2 and MnO2.

Chemism of the process is represented as:

MnO₂ + 2Cl₂ + 2H₂O + 3CaCO₃ Ca(MnO₄)₂ + 2CaCl₂ + 3CO₂ + 3H₂O

86,9     142     36         300          156              222          132        54

Table 1

Composition of manganese ore

Composition of carbonate ore during introduction of chlorine is presented in Table 1.

During introduction of a certain amount of chlorine into water suspension of carbonate manganese ore in order to receive HCl, mass of which equals 100 g, destruction of ore with receipt of the corresponding products takes place.

Table 2

The amount of product destruction in ore after introducing chlorine into suspension of carbonate manganese ore and formation of reaction products

Chemism of calcium carbonate destruction process during introduction of chlorine into suspension of carbonate ore for stabilization of pH solution is presented as the following reacion:

CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O

100 73 111 44 18

During introduction of a certain amount of chlorine, a certain amount of chlorous calcium (CaCl2) forms. The results are provided in Table 3.

Table 3

Dependence of chlorous calcium formation (grams) on the introduced chlorine into the system for destruction of calcium carbonate

Thus, solution of manganese oxide salt and chlorous calcium is retrieved from carbonate ore. This is how retrieving of manganese oxides are retrieved from ore. Disproportion of salt with receipt of Ca(MnO4)2 and MnO2 takes place in the solution. Oxidation of one molecule due to another molecule of the same substance is a common phenomenon in chemistry. It always goes on along with losses of free energy that is possessed by the system initially. Independent reaction is defined by the fact that free energy of the system in the end of reaction is lower than it was in the beginning of it. Condition, described by the lowest amount of energy is the most stable.

Under a careful examination one can see that flow of a chemical reaction is not defined by general amount of energy, but free energy.

Table 4

Dependence of manganese compounds lixiviation on addition of chlorine into reaction area

The fact that calcium manganite solution of manganese acid, in which manganese valency equals six, decomposes easily, point us to the conclusion that free energy in a system that consists of four- and seven-valent manganese, is lower than free energy that is contained in a system that keeps all manganese in six-valent form. However, conditions are usually opposite, and the state of intermediate valency proves to be the most stable condition. Thus, permanganate and salt of bivalent manganese react and form four-valent manganese.

Conclusion

While analyzing the research results, we can establish a possibility of simultaneous receipt of permanganates with the following obtaining of highly-concentrated manganese dioxide of no less than 85 %, as well as possibility of retrieving only manganese oxides from impoverished carbonate ore.

References

1. Kuzmin A.P. Methods of synthesizing potassium permanganate // Messenger of TSTU. – 2012. – Vol. 18, № 2. – Р. 387.
2. Palchick N.A., Grigorieva T.N., Moroz T.N. Natural and synthesized Mn-minerals // Magazine of non-organic chemistry. – 2013. – Vol. 58, № 2. – P. 172-177.
3. Posin M.E. Technologies of mineral salts in 2 parts, P. 1. – ed. 4, corrected. – L.: Chemistry, 1974. – P. 792.
4. Smirnova M.G. Electrosynthesis of oxidants and reductants / M.J. Fioshin, M.G. Smirnova. – Ed. 2, reviewed and enriched. – L.: Chemistry, 1981. – 212 p.
5. Pat. 4853095, United States, Int. Cl.: C25B 001/28. Conversion of Manganese Dioxide to Permanganate / D’Ambrisi Joseph J.; Assignee: MacDermid, Incorporated (Waterbury, CT); Filed on March 9, 1988 as Appl. No.: 165752, Prior Publication US August 1, 1989.