Roasting of gold ore samples, often an important step in the wet and wet extraction of gold was measured. Some researches have been carried out at home and abroad. With the deepening and development of practice, it is necessary and beneficial to carry out more systematic and in-depth research and understanding on some of its main problems.
First, the meaning of roasting
1. Roasting is beneficial to the complete leaching and dissolution of gold.
Direct leaching or dissolution of the gold ore, though more easy, it is generally only suitable for high degree of oxidation, a sample free of organic carbon, however, in most cases, samples often contain a sulfide, arsenic compounds, and organic compounds hoof Some gold organic carbon in the sample up to 7%, some of the organic matter (carbon, humic acid, etc.), sulfides (pyrite, yellow copper ore, black Au copper, bismuthinite, galena, etc.), Arsenic (toxic sand, etc.) is often a carrier mineral of gold. When these minerals are present in a large amount, such as treatment with a mixed solvent containing an oxidizing agent, the effectiveness, economy, safety, and ease of handling are far less than the calcination method. This is because mixed solvents often cannot oxidize sulfur and arsenic to high valence, and some sulphur is only oxidized to a single state. They also cannot completely and completely remove organic matter, and some organic substances are converted into elemental carbon or nitro derivatives. Because these substances have strong reducibility, adsorption, encapsulation or complexation, the gold can not completely enter the solution, and the leaching rate is obviously low. The calcination can completely remove organic matter, sulfur and arsenide, which is beneficial to the leaching and dissolution of gold. In addition, the calcination can also cause some of the aqueous minerals to lose crystal water, and many voids and channels are formed in the ore particles, so that the sample is porous and the surface is greatly increased. Calcination also breaks some inclusions, allowing the solvent to better contact with gold, and is also beneficial for gold leaching and dissolution.
2. How to eliminate or reduce the influence of some interferences?
Calcination can also remove mercury , bismuth , antimony, etc., which interfere with gold measurement by some methods, and can cause silver to form silver silicate which is hardly soluble in acid, reducing silver.
3, roasting can reduce the consumption of flux
Since roasting removes low-priced sulfur, arsenic and organic matter, and oxidizes metallic iron (introduced during sample preparation), low-cost iron, low-priced copper, etc. to a high price, it can save a large amount of oxidant and shorten the gold leaching cycle. .
Second, roasting is a complex process
Due to the large sample size of the sample, the large number of samples processed at the same time, and the limited oxygen supply, although some minerals are oxidized in the initial stage of roasting in air, the reducing atmosphere dominates the entire furnace. At this time, sulfides, arsenides, organic matter, etc. will be mainly pyrolysis:
Chalcopyrite CuFeS2=CuS+FeS
2CuFeS2=Cu2S+2FeS ten S↑
Pyrite FeS2=FeS+S↑
7FeS2=Fe7S8+6S↑
Bornite Cu5FeS4=CuS+2Cu2S+FeS
2Cu5FeS4=5Cu2S+2FeS+S↑
Pyrrhotite FenSn+3=nFeS ten S↑
Tonglan 6CuS=3Cu2S+3S↑
Black bismuth copper ore 4Cu2S.Sb2S=4Cu2S+Sb2S3
Wheel mine 3PbS·Sb2S3=3PbS+Sb2S3
Toxic sand FeAsS=FeS+As↑
The organic matter becomes an activated carbon which is relatively chemically stable and has reducibility and adsorption to gold:
CX(H2O)y=xC+yH2O↑
In addition, certain high-priced compounds may be reduced:
BaSO4+2C=BaS+2CO2↑
CaSO4+2C=CaS+2CO2↑
Some pyrolysis products will recombine:
As+S=AsS
As the reducing material is continuously decomposed and removed, and the furnace is continuously supplied with oxygen and warmed, the furnace gradually turns into an oxidizing atmosphere. At this time, sulfides, arsenides, organic substances, etc. are gradually oxidized:
Tonglan 2CuS+O2 = Cu2S + SO2↑
Copper ore 2Cu2S+3O2=2Cu2O+2SO2↑
Cu2S+2O2=Cu2O+5SO2↑
4Cu2S+10O2=4CuSO4+4CuO
Metal copper 4Cu+O2=2Cu2O
Copper ore 2Cu2O+O2=2Cu2O
Metal iron 2Fe+O2=2FeO
Ferrous oxide 4FeO+O2=2Fe2O3
Gemstone Ag2S+O2=2Ag+SO2↑
Cinnabar HgS+O2=Hg↑+SO2↑
Iron sulfide 3FeS+5O2=Fe3O4+3SO2↑
Elemental arsenic 4As+3O2=2As2O3↑
Stibnite 2Sb2S3 + 9O2 = 2Sb2O3 + 6SO2 ↑
Activated carbon C+O2=CO2↑
Realgar AsS+O2=As↑+SO2↑
Estraco As2S3+3O2=2As↑+3SO2↑2As2S3+9O2=2As2O3+6SO2↑
Some minerals that are not completely pyrolyzed are also gradually oxidized:
Pyrite 3FeS2+8O2=Fe3O4+6SO2↑
4FeS2+11O2=Fe2O3+8SO2↑
Pyrrhotite FenSn+3+O2=nFeS+SO2↑
Toxic sand FeAsS+3O2=FeAsO4+SO2↑
Certain minerals will interact with certain reaction products, such as pyrite, which interacts with ferric oxide, sulfur dioxide, and charcoal;
FeS2+16Fe2O3=11Fe3O4+2SO2↑
3FeS2+2SO2=Fe3O4+8S↑
3FeSO2+12C+14O2=Fe3O4+12CO2↑+6S↑
Some minerals in the sample can also interact:
2Ag2S+2SiO2+3O2=2Ag2SiO3+2SO2↑
2CaF2+SiO2=SiF4↑+2CaO
CaCO3+SiO2=CaSiO3+CO2↑
Some of the reaction products will also be recombined:
4Fe3O4+6As2O3+7O2=12FeAsO4
FeS+10Fe2O3=7Fe3O4+SO2↑
In summary, during the calcination process, some of the minerals will undergo pyrolysis, dehydration, oxidation (reduction), volatilization, recrystallization, recombination, and calcination is an extremely complicated process. Therefore, controlling the appropriate conditions and optimizing the calcination is a problem worth studying.
Third, roasting mud and heating rate
Experiments show that although the temperature at which some organic substances, sulfides and arsenides start pyrolysis oxidation is generally 200-550 ° C, the calcination temperature is lower than 600 ° C, the organic matter is not easily removed, and the residual amount of sulfide is also large, such as the calcination temperature is greater than 700 deg.] C, although beneficial organics, sulfides pyrolytic oxidation, in particular, can accelerate the decomposition of a high thermal stability sulfide (galena, sphalerite, etc.), but often causes contraction of the volume change and certain minerals crystalline , causing the melting of certain substances (see Table 1 for the melting point of several substances), and exacerbating the reaction between certain minerals, which not only causes the sintering of the sample, but also causes the soluble silicic acid to increase rapidly, interfering with the determination. When the sintering is not serious, the sample can be re-pulverized and analyzed. If the sample is severely sintered, it will be glazed on the porcelain boat wall. Even if the sample is re-pulverized, the measured result is still seriously low. In addition, the excessively high calcination temperature makes arsenic arsenate remain in the calcine, affecting the determination of gold and the recovery of arsenic. A large number of practices have shown that for the analysis of the sample roasting temperature, generally 600 ~ 650 ° C is appropriate, for the chemical smelting sample, due to its coarse particle size, the test sample is large, the roasting temperature can be slightly higher. However, it should not be more than 750 °C.
The temperature of the sample entering the furnace should be controlled below 200 ° C, and the heating rate should be less than 500 ° C / h. If the temperature is too high when the furnace is introduced, the heating rate is too fast, and the arsenic gold tends to form a low-boiling alloy volatilization loss, which tends to shrink the mineral volume, reduce the specific surface area, and also reduce the effects of removing carbon, arsenic and sulfur, especially low melting point. When minerals. The high temperature causes them to melt and coat the carbon, sulfur, arsenic, etc., making the baking difficult to complete and affecting the leaching and dissolution of gold. A large number of experiments have shown that the use of low temperature, long-time slow calcination, higher temperature, short-time rapid calcination is more effective, even if some minerals with high thermal stability will gradually oxidative decomposition after a long time of roasting.
Melting points of several substances Table 1
Substance name | Molecular formula | Melting point °C | Remarks |
Metal lead | Pb | 327.5 | |
Metal tin | Sn | 231 | |
Metal enamel | Sb | 630.5 | |
Cadmium metal | Cd | 321 | |
Metal zinc | Zn | 419.4 | |
Metal enamel | Bi | 271 | |
Lead oxide | PbO | 888 | |
Lead dioxide | PbO 2 | 290 | Decomposition and melting |
Lead tetraoxide | Pb 3 O 4 | 500 | Decomposition and melting |
realgar | AsS | 320 | |
Orpiment | As 2 S 3 | 310 | |
Glow mine | Sb 2 S 3 | 550 | |
Yan Hua | Sb 2 O 3 | 636 | |
Yan Hua | Bi 2 O 3 | 800 | |
Glow mine | Bi 2 S 3 | 685 | |
Lead silicate | nPbO.SiO 2 | About 700 | n=1~6 |
Fourth, roasting and mineral combination
The calcination effect of the sample is closely related to the mineral combination. For example, a quartz type sample has a good sulfur removal effect and does not sinter. The pyrite-type sample is also very good in roasting and desulfurization. However, the calcite -pyrite sample has a poor sulfur removal effect. We pyrite calcium magnesium salt of charcoal mixture consisting of a series of fired under the same conditions. Experiments show that some of the sulfides remain in the calcined sand. The residual rate of sulfur is the highest in calcite, followed by dolomite, and the smallest in magnesite . And the residual amount of sulfide is positively correlated with the content of these minerals. The calcium and magnesium phosphate and silicate calcined administered influence the sulfur removal. Calcium and magnesium sulfates generally have no effect on roasting and desulfurization. Only when the content of organic matter in the sample is high, the oxygen supply to the furnace is insufficient, and the temperature of the sample is too high, part of the sulfate is reduced to sulfide, which has an adverse effect.
When roasting certain lead or bismuth and tin, the sample contains more organic matter, and the metal iron (sample introduction) sometimes precipitates a metal melt, which traps gold at the bottom of the porcelain boat. Part of the lead oxide and the silicon in the test and porcelain boats, when the lead oxide and copper oxide coexist, the role is even more, due to the formation of a low melting point (about 700 ° C) of the vitreous:
nPbO+SiO2=nPbO·SiO2(n=1-6)
The gold is firmly bonded, wrapped, and enclosed at the bottom of the porcelain boat. This phenomenon is more serious when the sample is heated and calcined at a high temperature, making leaching and decomposition difficult.
V. Segmental roasting
In order to find out the effect of a batch of roasting and segmental roasting to remove sulfides, take -180 mesh pyrite and calcite ceramic crucible, stir well, place a muffle furnace at 650 ° C for a period of roasting and 490 ° C ± 10 ° C After calcination for 0.5 hour, and then heating to 650 ° C for partial calcination for 1 hour, take out and cool to room temperature, transfer the sample to a 500 ml flask, accurately add 200 ml of water, and shake it for 30 minutes on an electromagnetic oscillator (QZD-1 type). , to stand overnight, the following day the supernatant was drawn 100m1 to 250m1 flask, accurate iodine solution was added 0.02m1 20m1, 5m1 of acetic acid was added ice, placed in the dark for 3 minutes, Huai titration with standard sodium thiosulfate to light 0.01mol Yellow, add 1% starch solution 3m1, continue titration until the blue color disappears, and simultaneously carry out a blank experiment to calculate the sulfur content of the water-soluble sulfide. It can be seen from the results obtained in Table 2 that the effect of the staged calcination in addition to the sulfide is significantly better than that of the first stage of calcination. The content and recovery of gold obtained by segmental calcination are also significantly higher than that of a section of calcination. This is because a batch of calcination is prone to volatilization loss of gold arsenic alloy in arsenic-containing samples. It is easy to form alkaline earth metal sulfide with high thermal stability for sulfur-containing samples.
Such as calcium sulfide, etc., interference measurement.
Desulfurization effect of a section of initial burning and segmental roasting
Mineral addition amount (g) | Sulfur content in water soluble sulfide (mg) | ||
Pyrite | Calcite | a section of roasting | Segmental roasting |
1.0000 | 0.0000 | 0.00 | 0.00 |
1.0000 | 0.0500 | 0.83 | 0.00 |
1.0000 | 0.1000 | 1.55 | 0.05 |
1.0000 | 0.2000 | 2.27 | 0.08 |
2.0000 | 0.2000 | 3.35 | 0.10 |
2.0000 | 0.1000 | 1.96 | 0.08 |
CaCO3=CaO+CO2↑
CaO+FeS2=CaS+FeO+S↑
CaO+FeS2+O2=CaS+FeO+SO2↑
The calcination is carried out by first decomposing the sulfides such as pyrite and the sulfur and sulfur dioxide and sulfur trioxide at a temperature below 500 ° C. At this time, the calcite has not been decomposed, so it does not act with sulfur and has no sulfur fixation. In the first stage of calcination, the decomposition of arsenide is similar to the decomposition of sulfide. The decomposition of arsenopyrite is removed by the removal of monomeric arsenic and arsenic trioxide. Due to the low temperature, the chemical activities of gold and arsenic are low, they do not act, and do not cause gold. Loss. When the second stage of calcination is carried out at 650 ° C, the carbonate of the alkaline earth metal such as calcite or dolomite is partially decomposed, and since most of the sulfur has been removed, the formed calcium sulfide is minute. In addition, the segmental calcination greatly reduces the arsenate remaining in the calcine, which is beneficial to increase the recovery of arsenic and to reduce the interference of arsenic on the analytical gold.
Segmented calcination also avoids sintering of the sample. For example, a sample of calcined stibnite is prone to the phenomenon that stibnite (melting point 550 ° C) is not completely decomposed, that is, melting first to bond the sample, and by segmental roasting, the stibnite is firstly made at 490 ° C ± 10 ° C. All of the oxidation is enthalpy, and the temperature is further increased to 600 ° C to completely remove organic matter and other sulfides, which avoids sintering of the sample due to melting of the stibnite.
Six, combustion improver
In order to prevent sintering from forming into pieces and shortening the firing cycle, magnesium nitrate is generally recommended as a combustion improver in the literature. I have found that certain mineral or mineral decomposition products promote the decomposition of certain thermally stable sulfides. If a single galena is calcined at 650 ° C for 2 hours, the decomposition rate is less than 10%, and the same amount of the above minerals is mixed with an appropriate amount of pyrite or hematite or soft ore, and is still calcined under the above conditions. The decomposition rate can be increased to about 80%, which may be caused by the following reactions, which promote the pyrolysis and oxidation of sulfides.
4FeS2+11O2=2Fe2O3+8SO2↑
PbS+3Fe2O3+O2=2Fe3O4+PbO+SO2↑
4Fe3O4+O2=6Fe2O3
PbS+4MnO2=Pb0+4MnO+SO3↑
4MnO+O2=2Mn2O3
PbS+3Mn2O3=6MnO+PbO+SO2↑
PbS+4Mn2O3=8MnO+PbO+SO3↑
During the roasting process, a lead sulfate protective film is formed on the surface of the galena, which affects the continued oxidative decomposition of the galena. When iron oxide is present, it forms lead ferrite with lead sulfate or lead oxide, thereby improving the galena. Decomposition rate.
nPbSO4+mFe2O3=nFbO·mFe2O3+nSO3↑
When the soft oxidant Meng ore, the major product is calcined manganese oxide, and decomposition of its role hydrochloric acid added to produce sample dissolves gold chloride, thus saving the amount of the oxidizing agent.
Mn2O3+6HCl=2MnCl2+Cl2+3H2O
2Au+3Cl2+2HC1 2HAuCl4
In summary, due to the complex and variable chemical composition of gold ore samples, reasonable roasting conditions and parameters should be established for the ore characteristics.
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