«The investigation of the extraction of noble metals from sulphide ores by the sulphite – bisulphite – tiosulphate solutions»




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Taraz Kazakh -Turkish high school for gifted girls

named Aisha Bibi





«The investigation of the extraction of noble metals from sulphide ores by the sulphite – bisulphite – tiosulphate solutions »









Summary



On the scientific chemistry project «The investigation of the extraction of noble metals from sulphide ores by the sulphite – bisulphite – tiosulphate solutions » carried out by Mustafaeva Aygerim and Iskakova Alina, the students of the 10th

grade of the Kazakh – Turkish boarding – school for gifted girls named Aisha Bibi.


The process of the interaction of sodium sulphite with the sulphur containing product – the waste product from the oil-gas raw material of the Tengiz deposit has been investigated. It has been stated that pretreating of the Tengiz sulphur with the 0,3% sodium hydroxide solution positively influences the reaction velocity. The accelerating role of the sodium hydroxide solution can be interpreted as the ability of the hydroxide ions to activate the sulphur atoms resulting in the formation of the intermediate compounds – polysulphide that catalyst of the sodium and ammonium tiosulphate formation.

The sodium and ammonium tiosulphate, sulphite, bisulphite solution are the perspective, ecologically harmless reagents for gold and silver extraction from sulphide ore, substituting the toxic CN-containing solutions.

The process of oxidation exposition of sulphide ore of Akbakay deposit have been investigated and aimed for the increasing extraction of the noble metals output.

The effectivity and expediency of the application of sodium and ammonium tiosulphate – sulphite and sulphite – bisulphite solutions in the gold extraction technology have been shown.



  1. Introduction.

    1. Extraction gold from waste products of ore.

The purpose of our project:

To relieve our world from harmful and toxic cyanide solutions, from which investigate

noble metals. And replace it with pure ecologically clean and safe sulphite.

Republic of Kazakhstan have a lot of stores of noble metals and although a huge economical potential for dynamic development of national economy in ХХI century.

In the middle of variety of noble metals the main place takes gold, silver, platinum – they take an active role in economy of our country. In our world one of the most important problems is the ecology of our world and people which live there, but we must to put it to the first place by a lot of projects and ideas. In our days students try to improve our technology and to improve the ways how to make the world harmless and safe. We tried to solve this problem in gold industry. In our days there are a lot of solvents and ways for extracting gold, but after a lot of investigations we decided that most of them are harmful and the main way is extraction of gold by cyanide solutions.

The cyanide solutions are harmful for us and for ecology. Disavantages of cyanide solutions are:

1) Containing of gold more than 0.9 g

2) Cyanide solutions are not so strong

3) Tying of cyanide and oxygen with active pyrromones

4) The concentration of sodium cyanide is 0, 06-0, 0,8%.

5) High toxic properties

The cyanide process is very popular in metallurgy. It has so many disadvantages and one of them is that it is very toxic. So, our aim is that we must to find useful, safe, cheap reagent for extracting gold. After a lot of investigations we decided to discover other reagent that is safe and cheap. In Atyrau region the ecology is not controlled. The first problem they have is petrol; the second is the waste material of Tengiz deposit. This problem prevents to live easier. From this material scientist can make bombs, but we must to prevent them from making bombs. We found decision for two problems. The decision is to make safe, cheap, useful reagent, in place of cyanide solutions, from Tengiz sulphur, waste product from the oil-gas raw material of the Tengiz deposit. We suggest you to make the sulphite-bisulphite-tiosulphate solutions. These solutions were used in XX century. We calculated the constant of the reaction and they shows that the reactions are possible. Sulphite dissolving of noble metals in normal temperature allows us to minimize consumptions of very expensive reagents (solvent -6-7 times, oxid. -5times). One of the methods of obtaining sodium tiosulphate is the reaction of sodium sulphite with sulphur.

We have conducted research into reaction of sodium sulphite with sulphur containing product – the waste product from the oil-gas raw material of the Tengiz deposit (tengiz sulphur) and elementary sulphur. If we did all of this processes with elementary sulphur there will be formed polytionates (sodium tetrationate Na2S4O6 and sodium pentationate Na2S5O6) [43-44]. This polytionates are not stable, so they decompose and form elementary sulphur, which make worse product.

Also we investigated oxidizing of gold containing concentration. After oxidizing the result will be more useful for us. If we will compare two types of methods of extracting of gold: by cyanide solutions we can get 71% of gold, but by sulphite-bisulphite-tiosulphate solutions we can get 94-98%.

By these indicators we can say that sulphite-bisulphite-tiosulphate solutions are cheaper and competitive that cyanide and competitive.


The scientific novelty of this work is:


  1. Establishment of regularity of interaction of harmless sulphite– tiosulphate solutions with ore.

  2. Investigation of thawing of persistent gold ore for the first time.

3) The affectivity and expediency of the application of sodium and ammonium tiosulphate – sulphite and sulphite – bisulphite solutions in the gold extraction technology have been shown.





2. Literary view.

2.1. Dissolving of gold in tiosulphate solutions.

Thermodynamics of process.

There you can see thermodynamic calculations, which prove that the metallic gold can easily dissolve in tiosulphate reagents and in 21-23 literature behavior of gold in tiosulphate environment was given. The gold with tiosulphate ions produce stable complex, which will not give sulphur when we will add acid, from it can be taken H3Au(S2O3)2 ∙ ½H2O acid [24].

It is given that the reaction of gold with tiosulphate solutions is:

2Au + 4 + + ½O2 = 2Au () + 2OH.

Energy of Gibbs (isobaric-isothermal potential) of this reaction ΔG0 = -58, 35 kJ/mol. From this the equation of the reaction is:

Lg Kp = 58353, 73 / (2,3∙298∙8,31) = 10,23;

Kp = 1, 7 ∙ 1010.

This reaction can be shown by Zhuchkovs calculations:

2Au + 4 – 2e = 2[Au (S2O3)2] 3- ;

H2O + ½O2 p-p + 2e = 2OH, ΔG0 = – 77459 kJ/mol;

½O2 газ = ½O2 р-р , ΔG0 = – 8256,7 kJ/mol;


2Au + 4 + H2O + ½O2 = 2[Au(S2O3)2]3– + 2OH ,

ΔG0 = – 58353,7 kJ/mol.

So for this reaction:

2Au + 4 – 2e = 2[Au (S2O3)2] 3–

The energy of Gibbs is:

ΔG0 = - 58353,7 - ( -77459 - 8256,7) = +27362 kJ/mol.

By the equation ΔG0 = nFε we calculate the normal potential in tiosulphate:

ε0 = ΔG0/nF = 27362 / (2 ∙ 96485) = +0,142 В.

[Au (S2O3)2]3–

Au= Au+ + 2 ,

Kн = / .

= Kн · / lg = lg Kн + lg / .

εAu = 1,68 + 0,059 lg = 1,68 + 0,059 lg Кн +0,059 lg / .

/=1 In tiosulphate solution the potential is getting ε0 = +0,142 В.

1,68 + 0,059 lg Kн = 0,142 и lg Kн = –1,538/0,059 = –26,06.

Kн = 10-26.

All calculations was made at STP, we must to calculate in real situations because the results are not equal. Lets calculate in unacceptable conditions: the concentration of gold is 10-3 моль/л (or 200mg/l); concentration of oxygen – 10-4 mol/l (or 3,2 mg/l); concentration of hydroxyl ions – 10-2 моль/л (or 170 mg/l); concentration tiosulphate – 0,5mol/l. In these conditions the potential of the gold is:

ε = 0,142 + 0,059 lg (10-3/0,5∙0,5) = 0,142 + 0,059 (–3) – 0,059 lg 0,25 = – 0,058 В,

Then:

ΔG298 = ΔG0 + 2,3RT log [Au(S2O3)23-]2 ∙ [OH-]2 / [S2O32-]4 pO2½

ΔG298 = –81102,2 kJ/mole, Кр = 1,3 ∙ 1014.

When we will heat sodium tiosulphate the one of its products can be S2–, which by hydrolysis is getting SH:

S2– + H2O = SH + OH–.

The product of hydrolysis is hydrosulphide which can be the extra solvent.

Results of our calculations show us that the oxidation of gold by oxygen is real:

2Au + 2SH + ½O2 = 2[AuS] + H2O ,

ΔG0 = –173,3 kJ/mole.

Mechanism of the reaction will be different: oxygen can be depolarizer or oxidize sulphide hydrosulphide ions, to do polysulphide products, which although can react with gold by the help of oxygen:

2Au + = 2[AuS] , ΔG0 = 11,4.

Кр = [AuS]/ [] = 10-2 kJ/mole.

In this reaction if the concentration of the solution will be low the condition will be more suitable.

The silver with tiosulphate ions form very stable complex. It is well known that in XX century people used this solution to take gold from the ore.

It is the reaction of silver ethylsantogenete with tiosulphate.

AgC2H5OCSS + 2= + C2H5OCSS

Кр = 3,7 ∙ 10-4

ε = ε0 + 0,059 lg. [Ag(S2O3)2]3- = Ag+ + 2S2O32-;

Kд = / .

= ∙ 10-20

In normal conditions the potential of the gold in tiosulphate:

ε0 = +0,8 – 0,059 × 20 = - 0,38 В.

2Ag + 4 – 2e- =

ΔG0 = nFε0 = –2×96485×0,38 = –73328,6 J/mole

In these conditions the probability of the reaction is more than gold:

2Ag + 4 – 2e =;

ΔG0 = – 73328,6 J/mole.

H2O + ½O2 p-p + 2e = 2OH;

ΔG0 = – 77459 J/mole;

½O2 gas½O2 р-р;

ΔG0 = – 8256,7 J/mole;

2Ag + 4 + H2O + ½O2 = 2 + 2OH;

ΔG0 = – 159040,8 J/mole.
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