The amalgamation method has a long history of gold selection and has accumulated a wealth of production experience. However, people lack systematic research on the principle of amalgamation. Only in recent decades, the theoretical research on amalgamation of gold has made great progress.
Mercury commonly known as "mercury", which at room temperature is a silvery white liquid. If the surface cleansing natural gold particles are in contact with mercury, they will combine with mercury or be surrounded by mercury to form a “mercury paste”. The solid amalgam is alloyed to form three compounds; AuHg 2 , Au 2 Hg and Au 3 Hg, which also form a solid solution containing up to 16.7% of mercury in gold. In fact, the amalgamation gold selection operation is carried out in the slurry, and the amalgamation process is closely related to the three-phase interface properties of gold, water and mercury. It includes two processes of mercury infiltration of gold and amalgamation.
1. Mercury infiltration of gold The essence of the amalgamation process is that after the gold particles separated from the monomer are in contact with mercury, the metallized mercury removes the surface of the gold particles and rapidly wets the surface of the gold particles, and then the metal mercury is gold. The internal diffusion of the particles forms a gold amalgam-mercury paste. The greater the tendency of metallic mercury to remove the surface hydration layer of gold particles, the faster the speed, the more easily the gold particles are wetted by mercury and captured by mercury, and the higher the recovery rate of gold. Therefore, the primary condition for amalgamation of gold particles is that mercury can wet the surface of gold particles when gold particles are in contact with mercury, thereby capturing gold particles. Therefore, the infiltration of mercury into gold is carried out in an aqueous medium and can be represented by Figure 1. Mercury is incompatible with water, so in the amalgam system, there are two liquid phases, water and mercury, and a solid phase of gold.
It can be seen from Fig. 1 that mercury infiltrates on the gold particle surface to form a hemispherical surface, which creates a three-phase contact point between the gold particles and mercury and water, forming three interfacial forces, namely the interface between water and mercury. Tension, σ mercury-water , water-gold interfacial tension σ gold-water , and interfacial tension between mercury and gold, σ mercury-gold . When the gold particles in the slurry contact with mercury, a gold-mercury-water three-phase contact is formed, and the degree to which the gold particles are wetted by the mercury can be expressed by the wet contact angle of the mercury on the surface of the gold particles. If the angle between the mercury-water interface and the mercury-gold interface is specified as the wetting contact angle (θ) of mercury on the surface of the gold particles, it can be seen from Fig. 2 that the smaller the wetting contact angle θ of mercury on the surface of the gold particles, the smaller the gold particles. The surface is more susceptible to being wetted by mercury. Therefore, the surface of the gold particles has the characteristic of hydrophobicity of mercury, and the hydration layer on the surface is easily removed by mercury and wet by mercury; the surface of other minerals has the characteristics of mercury-hydrophilic, and the hydration layer on the surface is not easily eliminated by mercury. Mercury is wetted. The surface of the gold particles can be selectively wetted by amalgamation to separate the gold particles from other ore particles.

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The wetting contact angle θ is related to the surface energy of the gold-mercury-water three-phase interface. Let σ gold-mercury , σ gold-water and σ mercury-water represent the surface energy of each interface respectively; and regard it as surface tension (the two values ​​are the same, the units are different), then the following can be obtained from Figure 2(a) Relationship:

It can be seen that the relationship between the wetting contact angle θ derived from Fig. 2(a) or Fig. 2(b) and the surface tension is the same. The smaller the wetting contact angle θ, the closer the cos θ is to 1, and the greater the wettability of metallic mercury to the mineral surface. Therefore, cos θ can be referred to as a mercury-mixable indicator, expressed as H, then:

Since the surface of the gold particles and the surface of the metal mercury are both hydrophobic, the surface tension of the gold-water interface and the mercury-water interface is large, while the gold particles and the metal mercury are both metal lattices and have a high density. According to the principle of similar compatibility, gold particles and mercury are both metals, and their properties are similar. The surface tension at the gold-mercury interface is small. Therefore, the closer the surface tension of the gold-water interface is to the surface tension at the mercury-water interface, the closer the mercury-mixing index H is to 1, and the more easily the gold particles are wetted by mercury and amalgamated. On the contrary, the greater the wetting contact angle of metallic mercury on the surface of the ore particles, the smaller the mercury-admissive index, and the surface is not easily wetted by mercury and amalgamated. Therefore, any measures that can improve the gold-water interface and the surface energy of the mercury-water interface (surface tension) and reduce the surface energy of the gold-mercury interface during the amalgamation process can improve the mercury-mixable index on the surface of the gold particles, which is beneficial to Gold amalgamation and increase the recovery rate of gold in the process of amalgamation.
The process in which gold particles are contacted with metal mercury, wetted, and amalgamated is shown in Figure 3. Let S gold-water be the surface area of ​​the gold particles before capture, S mercury-water is the surface area of ​​the mercury beads, and S' gold-water is the residual surface area of ​​the gold particles not wetted by mercury during the capture process, then the gold particles are wetted by mercury. The energy before and after is: [next]
E before = S gold - water · σ gold - water + S mercury - water · σ mercury - water
After E = (S gold - water -S 'Gold - water) · σ Au - Hg + S' gold - gold · σ Water - Water + (S mercury - water -S 'Gold - water) · σ Mercury - Water

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