There are many mechanisms for the adsorption of gold by activated carbon, and three are mainly introduced here.
First, the physical adsorption caused by van der Waals force
This theory holds that the decomposition of gold cyanide ions under certain conditions will produce insoluble gold nuclide neutral molecules, which will precipitate cyanide gold to charcoal due to the van der Waals force, the attraction between activated carbon and gold cyanide molecules. In the hole.
Second, chemical complex theory
This theory holds that there is electrostatic attraction between the gold cyanide anion [Au(CN) 2 ] - produced during the gold ore leaching process and the positive charge grid on the activated carbon, that is, the gold cyanide anion in the leachate is adsorbed by the activated carbon.
Third, electrochemical theory
Electrochemical theory believes that in the presence of oxygen, hydrated activated carbon will hydrolyze to form hydroxyl (OH - ) and hydrogen peroxide (H 2 O 2 ), and the hydrolysis reaction is
O 2 +2H 2 O+2e 
H 2 O 2 +2OH -
The reaction of cyanide in dissolving gold is as follows:
2Au+4CN - +O 2 +2H 2 O 2[Au(CN) 2 ] - +2OH - +H 2 O 2
Since the char provides one electron to obtain a positive charge during the hydrolysis process, the positively charged char will attract the negatively charged gold cyanide anion formed during the leaching process. However, electrochemical theory cannot explain why some neutral complex molecules such as mercury cyanide (HgCN 2 ) compete with reactive cyanide complexes for reactive groups.
The process of adsorbing gold by activated carbon is generally considered to be a diffusion control process. The diffusion rate of gold to activated carbon can be described by Fick's law
A([Au]-[Au] i )
Wherein the diffusion rate of d[Au]/dt-gold;
Diffusion coefficient of D-gold cyanide ion;
[Au]- concentration of gold cyanide ion in the main solution;
[Au] concentration of gold cyanide ion on the i -carbon interface;
The thickness of the δ-boundary layer;
The area of ​​the A-boundary layer.
The mass transfer process of gold cyanide complex ions adsorbed to activated carbon includes at least two steps: the first step is the diffusion of gold cyanide ions from the bulk solution to the surface of the carbon; the second step is the diffusion of gold cyanide ions from the carbon surface to the micropores. Active groups within. Therefore, when the activated carbon adsorbs gold, the carbon outer layer is first saturated, but the inner diffusion determines the rate of the mass transfer process.
Precision Manipulator
Linear Rail,Precision Manipulator,Ball Screw Linear Guide,Stainless Steel Linear Guide Rails
Guangdong TICO Automation Technology Co.,Ltd. , https://www.tico-robots.com