Principle of amalgamation gold selection (2)

The energy change of the system before and after wetting is:
_After â–³ E = E _before -E
=S _{gold -water} ·σ _gold-water +S _{mercury -water} ·σ _{mercury-water-} (S _gold-water- S' _gold-water )·σ _gold-mercury
-S' _gold-water ·σ _gold-water- S _{mercury-water} ·σ _{mercury-water} +S' _gold-water ·σ _{mercury-water}
=(S _gold-water- S' _gold-water )·S _gold-water- (S _gold-water- S' _gold-water )·σ _gold-mercury +S' _gold-water ·σ _{mercury-water}
=(S _gold-water- S' _gold-water ) (σ _gold-water- σ _gold-mercury )+S' _gold-water ·σ _{mercury-water}
Because S _gold-water ≥ S' _gold-water , σ _gold-water ≥ σ _gold-mercury ,
Therefore, △E>0, that is, the process of wetting the surface of gold particles reduces the energy of the system, and the surface energy of the metal mercury wets the gold particles automatically, and the difference between the surface energy of the gold-water interface and the surface energy of the gold-mercury interface The smaller the remaining gold-water boundary area that is not wetted by mercury, the greater the change in energy before and after the gold particles are wetted, and the more readily the surface of the gold particles is wetted by metallic mercury. Therefore, the energy change ΔE before and after wetting can be referred to as the wetting work or the trapping work of the surface of the metal mercury wetting gold particles, which is represented by WH:
WH=△E=(S _gold-water- S' _gold-water ) (σ _gold-water- σ _gold-mercury )+S' _gold-water ·σ _{mercury-water}
When S' _gold-water =0,
WH = S _gold-water ·(σ _gold-water- σ _gold-mercury )
If the gold particles and other minerals are in the form of continual organisms, the S _gold-water is the gold-water interface surface area in the continuous organism, and the S- _mine-water is the other mineral-water interface surface area in the continuum, then the continuum is wetted by mercury. The energy change is:
E _before = S _{gold - water} · σ _{gold - water} ten S _{mine - water} · σ _{mine - water} + S _{mercury - water} · σ _{mercury - water}
E _post = S _{gold - mercury} · σ _{gold - mercury} + S _{mine - mercury} · σ _{mine - mercury} + S _{mercury - water} · σ _{mercury - water}
△E=E _before- E _after =S _gold-water ·σ _gold-water +S _mine-water ·σ _mine-water- S _gold-mercury ·σ _{gold-mercury-} S _mine-mercury ·σ _mine-mercury
Because S _gold-water = S _gold-mercury , S _mine-water = S _mine-mercury ,
Therefore, △ E = S _{gold - water} (σ _{gold - water -} σ _{gold - mercury} ) + S _{mine - water} (σ _{mine - water -} σ _{mine - mercury} ).
Because σ _gold-water ≥ σ _gold- mercury, σ ore-water < sigma-mercury,
If S _gold- water≥S- _{mineral-water} , △E>O, the wetting process can be carried out automatically;
If S _gold-water "S _mine-water , â–³E Therefore, when the gold particles are in the form of continuum, only when the surface of the continuum is mostly gold, the metal mercury can automatically wet the gold particles in the continuum and capture the continuum. Otherwise, the metal mercury cannot automatically capture the gold particles; the gold in the living body is lost to the mercury tailings with the loss of the slurry. The gold particles present in the inclusions are not in contact with mercury and will also be lost in the amalgam tailings. Therefore, increasing the fineness of grinding and increasing the degree of dissociation of natural gold particles can often increase the recovery rate of gold in the amalgamation operation.
Therefore, any factor that can improve the surface energy of the gold-water interface and the surface energy of the mercury-water interface, reduce the surface energy of the gold-mercury interface, and improve the dissociation of natural gold particles can increase the mercury-mixable index of gold particles (H). ) and capture work (W _H ). That is, the more hydrophilic and hydrophobic the gold particles are, the more easily the gold particles are wetted by mercury and captured by mercury; the more hydrophilic and hydrophobic the surface of the metal mercury, the easier it is to wet the surface of gold particles and capture gold particles; natural gold particles The higher the degree of monomer dissociation, the higher the recovery rate of gold in the amalgamation operation.
Gold and silver in nature are generally symbiotic or associated, and the mercury paste obtained in the case of mercury is silver in addition to gold. The so-called selective infiltration of mercury by mercury does not mean that mercury only infiltrates gold and silver, but does not infiltrate copper , lead , zinc, etc., but the latter is mostly in the form of a compound and is not easily infiltrated by mercury.
Amalgamation process
After the mercury infiltrates the surface of the gold particles, the process of diffusion into the interior of the gold particles is called amalgamation. Gold and mercury have infinite solubility in liquid form. Even at room temperature, gold is still soluble in mercury. The process in which mercury infiltrates gold particles and diffuses into the interior of the gold particles to form various Au-Hg compounds can be represented by FIG.

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The outermost layer of gold particles is surrounded by mercury. The amount of mercury is large, forming AuHg ₂ , the outer layer forms Au ₂ Hg, the third layer forms Au ₃ Hg , the fourth layer only diffuses a small amount of mercury, and gold forms a gold-based solid solution. The core of the gold grain is not in contact with mercury and is still pure gold. The gold mercury paste produced by the amalgam method is a solid solution and a compound composed of mercury and gold.
The two-phase equilibrium diagram of mercury is shown in Figure 2. At 20 ° C, mercury can dissolve 0.06% of gold. The fluidity of mercury and the solubility of gold in mercury increase with the increase of temperature. At 20 ° C, gold can form a solid solution with 15% of mercury (atoms). The maximum ratio of gold mercury compounds is equivalent to a gold content of 84.7%. However, in actual production, it is impossible to achieve a balance between gold and mercury. The mercury paste scraped from the industrial production of mercury is generally covered with mercury (a composition of mercury-gold compounds equivalent to AuHg ₂ , Au ₂ Hg, and Au ₃ Hg). It consists of the remaining mercury-free gold and free mercury (excess mercury). Mercury paste is liquid when it contains less than 10% gold, and is dense when it contains 12.5% ​​gold. When coarse-grained gold is mixed with mercury, there is more gold remaining in the amalgamation, and the gold content of the industrial amalgam can reach 40%-50%. When fine-grained gold is mixed with mercury, the gold content is small, the specific surface area is large, the amalgamation is relatively complete, and the amount of free mercury attached is high. The gold content of industrial mercury paste can be reduced to 20%-25%. Generally, the gold content of industrial amalgam is close to AuHg ₂ The composition of the compound has a gold content of 32.93%. In addition, industrial amalgam contains other metal minerals, quartz , gangue debris and other mechanical mixtures and a small amount of amalgamated silver, copper and other metals.

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The extraction of gold from the ore is to use this special combination to make the gold-containing slurry contact with mercury, so that gold and mercury become "mercury paste", which is separated from other metal minerals and gangue minerals to achieve enrichment. The purpose of gold, gold is different from other metals in that it is mostly not a compound in the ore, but exists in a free state. When the gold ore is crushed and the particle size reaches 200 mesh and accounts for more than 65%, most of the gold can be obtained. Monomer separation, which does not easily form a stable three-phase contact angle when present in water, and can be preferentially infiltrated by mercury, so gold particles can be further immersed by mercury; conversely, particles that are preferentially wetted by water can also be The water is engulfed. This is the basic principle that amalgamation can select gold from ore.
Whether mercury can wet gold well depends mainly on the composition of gold and mercury, the surface state of gold and the quality of mercury, operating temperature, pulp concentration and pH of pulp.
The effect of gold amalgamation is directly related to the degree of dissociation of gold from the minerals enveloping it. Therefore, it is of great significance to choose a reasonable grinding operation. Under the premise of ensuring that the grinding is not excessively pulverized, appropriately increasing the fineness of the grinding will contribute to the improvement of the recovery rate of the mixed mercury. The relationship between the recovery rate of amalgamation and the type of gold ore and the fineness of grinding is shown in the table.

Pure gold is the easiest to mix with mercury. In addition to gold, gold particles in nature and ore contain impurities such as silver, copper, and iron , which makes it difficult to mix mercury. When gold is contained in gold, 10%, the ability to be infiltrated by mercury is significantly reduced.
The mercury amalgamation effect of pure mercury is also not good. Instead, a small amount of gold, silver and rhodium metal can improve its wetting properties. Mercury contains 0.1%-0.2% gold, which accelerates the amalgamation process. Mercury contains 0.1% silver, the ability to infiltrate gold can be increased by 70%, and the gold and silver content can be increased by 5%. The amount of copper, lead and zinc in mercury is less than 0.1%, respectively, which promotes the infiltration of mercury into gold. If there is an oxide film or other adsorption film on the surface of the gold particles, or it is contaminated by other minerals or gangue, it is difficult to wet the mercury, which will reduce the recovery rate of gold.

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