Gold ore mineral composition is varied, in addition to inert, non-functioning cyanide mineral (quartz, silicates, iron oxide), the oxygen can often present with cyanide and reacting the starting solution. They carry out side reactions, increase the consumption of reactants, and reduce the rate of leaching of gold and the rate of leaching. These side-reaction products can also make it difficult to work with zinc replacement gold. Therefore, the mineral composition of gold ore is one of the main factors determining the cyanidation index. Gold ores, it is common and strongly influence the effect of cyanide leaching minerals are: iron, copper, antimony, arsenic minerals; zinc, mercury, lead and other minerals, although relatively small, but can also affect the cyanidation process. Table 1  Dissolution of copper minerals in a mass fraction of 0.1% NaCN solution Mineral name Molecular formula Copper dissolution rate /% Natural copper Cu 90 100 Azurite 2Cu·CO 3 Cu ( OH ) 2 94.5 100 Copper mine Cu 2 O 85.5 100 Chrysocolla CuSiO 3 11.8 15.7 Copper ore Cu 2 S 90.2 100 Chalcopyrite CuFeS 2 5.6 8.2 Copper ore FeS·2Cu 2 S·CuS 70 100 malachite CuCO 3 ·Cu ( OH ) 2 90.2 100 Sulfur arsenic copper ore 3CuS·As 2 S 5 65.8 75.1 Beryllium copper mine 4Cu 2 S·Sb 2 S 3 21.9 43.7 Copper is complexed with an anion [Cu(CN) n+1 ] n- (n=1, 2, 3) in the solution. Under industrial conditions (free cyanide concentration 0.01% to 0.1%), mainly [Cu(CN)] 2- , followed by [Cu(CN) 4 ] 3- complex anion. The most common lead-containing mineral in gold-bearing ores is galena (PbS). The ore contains an appropriate amount of lead, which is often advantageous for the cyanidation of gold, since lead can eliminate the deleterious effects of alkali metal sulfides in cyanide. At the time of replacement, lead can form a zinc-lead partial battery on the surface of the zinc powder to promote precipitation of gold. Table 2  Effect of lead salt on gold dissolution under different lime dosages CaO dosage / ( k g · t -1 ) PbCO 3 PbSO 4 PbO NaCN consumption / ( k g· t -1 ) Gold dissolution /% NaCN consumption / ( k g· t -1 ) Gold dissolution /% NaCN consumption / ( k g· t -1 ) Gold dissolution /% 0 0.28 94 0.68 96.4 0.28 99.4 1 0.06 57.5 0.08 56.2 0.04 61.4 2 0.04 57.4 0.04 49.7 0.04 35.2 4 0.08 65.8 0.04 52.4 0.04 47.8 A few gold ores contain cinnabar HgS and bismuth mercury ore HgTe. There may be a small amount of metallic mercury and its oxides in the amalgam tailings. HgS dissolves very slowly during cyanidation. Similar to lead salts, when there is a small amount of mercury in the cyanide solution, the harmful effects of S 2- can be reduced. The film formed on the surface of the precious metal can be removed by mechanical action (such as the friction between the particles and between the particles and the wall). Therefore, the fatigue of cyanide is also related to the leaching method, and the most severe fatigue is percolation. The weakest is agitation, especially in the mill. Wood lathes can be used to create functional furniture components, beautiful decorative wood projects such as candlesticks and bowls, or even toys such as tops and yo yos. These machines range in size from hobby models that fit on a work bench to large industrial-sized machines weighing hundreds of pounds, but they all share some basic elements. Here are some instructions for using these unique machines. For those in the machining and turning crafts, it`s common knowledge that the Industrial Revolution had a significant impact on the evolution of the lathe and additional machine tools. As humans began developing tools and technology, honing new skills, and began more efficient ways of production, different power sources started to become standard. Motors now required electricity, meaning the conventional way of operating machine tools by human touch was being phased out as more and more machinists were [turning" to automation. But before automation and metalworking became regular practices in the machining world, there was woodturning and thus, wood lathes. Lathing Machine,Lathe Machine,CNC Lathe Machine,CNC Lathing Machine JINAN XUANLIN MACHINERY CO., LTD. , https://www.cncfiberlaser.com
1) Iron minerals Iron minerals in gold ore can be divided into two major categories of oxidized ore and sulfide ore. Hematite Fe 2 O 3 , magnetite Fe 3 O 4 , goethite Fe 2 O 3 ·H 2 O, siderite FeCO 3 etc. belong to oxidized ore, and this type of iron mineral does not act with cyanide No harmful effects on the cyanidation process. In contrast, iron sulfide ore, such as pyrite FeS 2 , pyrite FeS 2 , pyrrhotite Fe 1-x S (x = 0-0.2), occurs significantly during cyanidation and is sometimes very important. Changes have caused a series of adverse consequences. The stability of these sulfide minerals during cyanidation depends on their own crystalline structure, properties, particle size and cyanidation conditions.
The behavioral characteristics of iron sulfide ore in cyanidation are not so much the effect of cyanide solution and iron sulfide itself as they do with their oxidation products.
According to the speed of oxidation, two types of slowly oxidized and fast oxidized iron sulfide ore can be relatively divided. Most pyrite, especially those with dense, coarse-grained crystal structures (cubes and pentagonal dodecahedrons) belong to the former category. They oxidize very slowly and do not oxidize during the entire process including grinding and cyanidation. Therefore, it is usually not difficult to cyanide gold from such slow-oxidized pyrite.
The ore belonging to the second category is a fine-formed, loosely-structured iron sulfide variant, mainly pyrrhotite and most of the pyrite. In rare cases, pyrite containing fine crystals also falls into this category. They have a high oxidation rate and undergo significant oxidation during mining, transportation, storage, especially grinding and cyanidation. Treatment of such minerals will increase cyanide consumption and reduce gold recovery if no special measures are taken.
In order to eliminate these harmful effects of cyanidation of rapidly oxidized iron ore, the following main measures are used in production practice:
1 inflated in an alkaline solution before cyanidation; 2 strongly inflated during cyanidation; 3 added lead oxide or soluble lead salt in the cyanide slurry.
The first measure is based on the oxidation of ferrous sulfide to Fe(OH) 3 when aerated in an alkaline solution containing no cyanide:
4FeS+9O 2 +8OH - +2H 2 O=====4Fe(OH) 3 +4SO 4 2-
However, Fe(OH) 3 does not react with cyanide. [next]
The second measure is based on a pneumatic strongly promote oxidation of S 2- S 2 O 3 2- and SO 4 2- FeS with a corresponding reduction in cyanide, oxygen and generated CNS - the ratio of the portion of S 2-.
The third measure is to convert the dissolved sulfide (S 2- ) to thiocyanide.
Although the above measures can not completely eliminate all the hazards of fast oxidizing iron sulfide ore, after all, acceptable process indicators can be obtained.
2) Copper minerals In gold ores, copper minerals are often associated. They react with the cyanide solution to form a copper cyanide complex, causing a large consumption of cyanide. It is seen from Table 1: Except for the blue malachite, especially the chalcopyrite and cyanide, almost all copper minerals are quite completely and rapidly dissolved in the cyanide solution.
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As can be seen from Table 1 above, copper minerals are highly reactive with cyanide. Therefore, even if its content is very small (0.1%), it will cause a large consumption of cyanide, making it unprofitable to use the general liquefaction process to withdraw gold.
The difficulty in handling copper-containing minerals is far more than the high consumption of cyanide. More importantly, the presence of [Cu(CN) 3 ] 2- significantly reduces the dissolution rate of gold, thus reducing the recovery of gold. There are two explanations for this phenomenon.
First, when the copper cyanide solution, most of CN - ions forming copper [Cu (CN) n + 1 ] n-, thus remaining free CN - concentration is low, because the formation of more High coordination number of copper cyanide anion. In order to increase the rate of gold dissolution, it is necessary to make all the copper in the solution become [Cu(CN) 4 ] 3- ions. However, after doing so, it is still not possible to achieve the goal of accelerating leaching and increasing gold recovery. It shows the effect of copper cyanide process is complex, and is not limited to CN - formation of copper cyanide complex ion.
Second, the harmful effects of copper are not only to reduce the free CN - concentration, but also to form a film on the gold surface, which reduces the dissolution rate of gold. According to this theory, the free CN-concentration near the gold surface (in the diffusion layer) becomes so small that the dissociation equilibrium of the copper cyanide ion proceeds to the right:
[Cu(CN) 3 ] 2- =====[Cu(CN) 2 ] - +CN - =====CuCN↓+2CN -
Re-insoluble copper cyanide. The CuCN precipitate covers the gold surface, making it difficult for gold to enter the solution. It has been confirmed by accurate measurement of radioisotopes that in the copper-containing cyanide solution, copper is indeed present on the surface of the noble metal, and as the concentration of copper increases, the density of the film increases, and the dissolution rate of gold decreases accordingly. When the copper concentration in the solution is not high (mass fraction is less than 0.05%), the formed film has the characteristics of "inlaid", that is, it is positioned at the site with the highest surface activity. The film is porous, the solvent can enter, and the reaction product can also be It diffuses out, so it has little effect on the dissolution rate of gold.
According to the above, the copper-containing gold ore is often treated in a multi-stage dipping process. The last stage of leaching is adjusted with fresh water, which reduces the concentration of copper in the cyanide solution. When the cyanide concentration is low, the effect of copper minerals and cyanide is slow, and this property is sometimes used to treat copper-bearing gold ore. For high copper gold ore, pretreatment such as roasting and copper immersion must be carried out before cyanidation.
3) Arsenic and antimony minerals The most harmful minerals in the cyanidation process of precious metals are arsenic and antimony minerals. The strontium minerals are mainly stibnite (Sb 2 S 3 ), arsenic mineral toxic sand (FeAsS), orpiment (As 2 S 3 ) and realgar (As 4 S 4 ). [next]
The decomposition products of arsenic and antimony sulfide are accumulated in the cyanide solution: AsS 3 3- , SbS 3 3- , S 2- , AsO 3 3- , SbO 3 3- , and as a result, a dense film is formed on the surface of gold. hinder CN - and O 2 leading to the gold particles, thus making gold dissolution rate slowed sharply. This is the main reason why gold ore containing arsenic and antimony is extremely difficult to cyanide. The nature and formation mechanism of such membranes have not yet been clarified, only that their formation is related to the accumulation of the above ions in the cyanide solution.
Kinetic studies of the dissolution of Sb 2 S 3 , As 2 S 3 and As 4 S 4 indicate that their rate of dissolution is primarily dependent on the concentration of the protective base. Reducing the pH of the cyanide solution greatly reduces their decomposition rate. Therefore, when the gold ore containing arsenic and antimony sulfide is cyanated, the lowest possible concentration of the protective alkali should be used.
Another measure to cyanide this gold ore is to add lead salts to convert the decomposition products of arsenic and antimony in the solution into relatively harmless CNS - ions as quickly as possible.
It must be pointed out that arsenopyrite is one of the most widely associated minerals in gold ore. Unlike As 2 S 3 , it does not actually dissolve in the alkaline cyanide solution. Therefore, it does not have a bad influence on cyanide gold extraction. However, the arsenopyrite is often coated with particulate gold, and even in the case of ultrafine grinding, the encapsulated gold cannot be exposed. In this case, gold must be paid in a special way.
4) Zinc, lead and mercury minerals Gold ore generally contains little zinc minerals, mainly sphalerite (ZnS), and its presence does not substantially affect the cyanidation process. Sphalerite reacts slowly with cyanide solution: 
In the absence of oxidation, galena is weaker than cyanide, forming NaCNS and Na, PbO 2 , and lead oxide ore (PbO 2 ) can be dissolved by alkali in cyanide to form CaPbO 2 or Na 2 PbO 2 And reacting with soluble cyanide to form a PbS precipitate. It should be noted that excessive lead in the solution will also have an adverse effect on the leaching of gold. Especially when using lime as a protective base, the amount of lime should be controlled, and the leaching rate of gold will decrease significantly with the increase of the amount of lime. Table 2 shows the effect of different lead salts on gold leaching under various lime dosage conditions. [next]
5) Other minerals Gold ore may also contain selenium , tellurium and carbon compounds. Selenium is dissolved in the cyanide solution to form selenium cyanide.
NaCN+Se=====NaCNSe
The dissolution rate of selenium has the following relationship with the cyanide concentration:
NaCN concentration (mass fraction) 0.03% 0.06% 0.11% 0.25%
Selenium dissolved amount (mass fraction) 2.32% 7.18% 15.8% 31.2%
Selenium in ore has little effect on the dissolution rate of gold, but it increases the consumption of cyanide and makes it difficult to replace gold. In order to eliminate or reduce the harmful effects of selenium on the cyanidation process, the following measures can be taken:
1 Cyanide with a low concentration cyanide solution.
2 The activated carbon is used to precipitate gold from the cyanide solution or the slurry, because the presence of selenium in the solution has little effect on the ability of the activated carbon to adsorb gold.
3 The ore is calcined at a temperature of 600-700 ° C. During the roasting process, the selenium is almost completely volatilized, and then the calcine is treated by cyanidation. [next]
In gold and silver ores, minerals tellurium Te gold (AuTe 2) and tetradymite (Bi 2 TeS), tellurium poorly soluble in mineral cyanide solution but tellurium minerals in fine grinding, high alkalinity and Under a large amount of aeration, it can also be treated by cyanidation. In the cyanide solution, strontium is dissolved to form sodium hydride Na 2 Te, which in turn produces a sulphonate. As a result, the cyanide is decomposed and absorbs oxygen in the solution, and the cyanidation method is used to extract gold.
For the cyanidation of gold ore containing silver ore (Ag 2 S), in order to promote the dissolution of silver in the cyanide solution, the lead salt can be used to eliminate Na 2 S, and the reaction of the following formula is carried out to the right (complex silver-containing sulfuric acid) Except salt ore):
Ag 2 S+4NaCN=====2NaAg(CN) 2 +Na 2 S
The gold mine sometimes contains graphite . When cyanide dissolves gold, the Au(CN)2-gold complex ions in the solution are adsorbed by the carbon, so that the dissolved gold is returned to the ore with the carbon particles, resulting in a decrease in the recovery rate of gold. To prevent this effect, a small amount of cyanide may be added before kerosene, to inhibit the adsorption of carbon, or baking, the charcoal off.
6) Fatigue of cyanide solution The cyanide solution interacts with associated minerals, which not only increases the consumption of cyanide, but also causes a large amount of impurities to accumulate in the solution. When the cyanide solution is returned multiple times, the concentration of impurities can reach a very high value. The accumulation of impurities causes a decrease in the activity of the cyanide solution, that is, a phenomenon in which the ability to dissolve gold is lowered, which is called cyanide solution fatigue. When the impurities accumulate to a certain limit, the activity of the solution cannot be restored to its original state despite the addition of free cyanide.
The main reason for the low activity of the dirty cyanide solution is that various films are formed on the surface of the precious metal to hinder the dissolution process. The reason for the formation of the film, in addition to the chemical action of the impurities on the surface of the noble metal, is also due to the adsorption of the surface active substance present in the solution.
The passivation of the film is related to the structure (porosity) and thickness of the film, and the porosity and thickness of the film mainly depend on the nature and concentration of the impurities forming the film. For example, the complex anions of copper, zinc and iron in cyanide solution have the same mechanism for their formation: negatively charged [Cu(CN) 3 ] 2- , [Zn(CN) 4 ] 2- The metal anion such as [Fe(CN) 6 ] 4- is adsorbed on the surface of the gold particles to form a shield to prevent dissolution; at a low cyanide concentration, a simple cyanide film CuCN, Zn(CN) 2 , Fe(CN) is formed. 2 . However, the porosity of the films they form is quite different: the film formed by the copper compound is the densest, and the cyanide and oxygen are extremely difficult to penetrate; on the contrary, the iron compound forms a porous film and penetrates well; the zinc compound film is interposed Between the two. Correspondingly, the degree of passivation of impurities is also gradually increased in the order of iron-zinc-copper.
As described above, when a ruthenium or arsenic compound is present in a cyanide solution, a dense film is formed, which greatly reduces the dissolution rate of gold. Therefore, when there are stibnite, realgar, and orpiment in the ore, the fatigue of the cyanide solution is particularly severe.
When a protective base is added to the cyanide solution, its activity is also lowered. As shown, as the lime concentration c increases, the gold dissolution rate. decline. When caustic soda is used as a protective base, it has almost the same effect. The reason for this phenomenon is probably that a film is formed on the surface of gold. The nature of this film is not known. In order to reduce this "deceleration effect" of the protective base, the concentration of the protective base should be maintained at the minimum level necessary to inhibit the hydrolysis of cyanide. [next]
The fatigue phenomenon of cyanide is very complicated and far from clear. In particular, the passivation mechanism when several impurities are present at the same time remains to be studied.