The Heze activated carbon box achieves the purpose of purifying waste gas

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2 The adsorption process of activated carbon is completed in three steps: the outward diffusion of Au(CN)- toward the surface of the carbon particles, the inward diffusion into the interior of the carbon particles, and adsorption. 3. Factors affecting activated carbon adsorption 3.1 Type of activated carbon: The adsorption properties of coconut shell carbon and apricot kernel carbon are far superior to those of coal-based and coke-based carbon. 3.2 Structure of adsorption equipment: The common types of adsorption tanks are axial-flow and radial-flow types. Comparatively, axial-flow tanks have lower resistance, smaller dead zones, and a lower rate of carbon wear, especially when dual impellers are used. 3.3 The properties of the slurry refer to its particle size characteristics, concentration and viscosity, organic matter content, and pH value of the slurry. The particle size characteristics of the pulp refer to the fact that it often contains wood chips or coarse mineral particles larger than the pore sizes of the inter-stage screens; these particles can cause blockages in those screens and lead to a decrease in the grade of the gold-bearing carbon. Additionally, the desorption rate of gold-bearing carbon containing wood chips is also low. 　The concentration of the slurry primarily affects its specific gravity and fluidity, which in turn directly influence the floating ability of activated carbon as well as its uneven distribution, thereby hindering the adsorption process. Practice has shown that it is advisable to keep this concentration at an optimal level. The viscosity of the pulp is primarily determined by the amount of fine sludge present; the more sludge there is, the higher the viscosity, and the worse the fluidity, which can lead to clogging of the inter-stage screens. Additionally, both leaching and adsorption efficiency are reduced in such conditions. The organic substances in the pulp mainly include wood chips, oils, humic acids, flotation agents, etc. They can be adsorbed by activated carbon, affecting the adsorption rate of gold and poisoning the activated carbon, thereby complicating the activation and regeneration of the carbon. 3.4 Number of adsorption stages and bottom carbon concentration: The number of adsorption stages and the bottom carbon concentration are generally determined through experiments and experience. The number of stages is usually 4 to 6, while the bottom carbon concentration is kept within the range of 5 to 25 grams per liter. Countercurrent carbon stacking is used, in both intermittent and continuous modes. 3.5 Slurry aeration: An excessive amount of air in the slurry can reduce the leaching rate of gold as well as the adsorption of gold by activated carbon. The common methods of aeration are central aeration and pipeline aeration, and experience has shown that central aeration at the axis is superior. 　4 Carbon Extraction Equipment and Process Operations 4.1 The carbon extraction equipment currently in use includes turbine pumps, jet pumps, and air mixing chambers. 　　4.2 The carbon addition during process operation generally starts from the first tank, and then carbon is added sequentially to each subsequent tank; finally, carbon is added to the last tank. The number of times carbon is added is determined based on experiments and theoretical calculations, with consistency maintained across all shifts. 　　Desorption of gold from gold-loaded carbon 5.1 Principle of desorption of gold-loaded carbon Experimental studies have shown that the process of adsorption by activated carbon is actually a reversible one; when carbon adsorbs gold, high temperatures, pressures, pH values, and cyanide (CN—) concentrations can significantly reduce the amount of gold adsorbed. Therefore, it is entirely possible to use effective methods to desorb the gold from the gold-loaded carbon into the solution. 5.2 Desorption methods and process conditions for gold-loaded carbon 5.2.1 Normal-pressure heating desorption method (also known as the Zadrach desorption method) This is the simplest method that was developed first. At a temperature of °C, a mixed aqueous solution prepared from is passed through a gold-loaded carbon bed; it takes approximately hours to meet the desorption requirements. 5.2.4 The US-UK desorption method: This method was developed by the South African US-UK Research Institute. It involves pre-treating the gold-loaded carbon with a mixture of 5 and 1.0 volumes of a certain solution for several hours, followed by desorption using heated deionized water in an amount equivalent to 5 volumes of the gold-loaded carbon, at a flow rate of 3 volumes of the carbon bed per hour. The operating temperature and pressure are specified in kilograms per square centimeter, and the desorption time (including the acidic treatment phase) is approximately several hours. 5.3 Desorption Equipment and Operational Precautions The desorption equipment for gold-loaded carbon is usually connected to the electrolytic deposition equipment, forming a unit within the production cycle. The prepared gold-loaded carbon is placed into the desorption tower (column), and the prepared desorption solution is pumped into the desorption electrowinning system; the specific procedures depend on the equipment and process being used. 5.4 Points to Note for the Desorption of Gold-Loaded Carbon 5.4.1 When the length-to-diameter ratio of the desorption tower is high, the desorption effect is better, operation becomes easier, and the desorption time is reduced; therefore, towers with a length-to-diameter ratio that is high are generally used. 5.4.2 The flow pattern of the desorption liquid within the tower should be such that the flow velocity is evenly distributed across the cross-section of the tower, ensuring thorough contact with the gold-loaded carbon. 　5.4.3 The appropriate desorption time is determined through experimentation. Generally, the longer the desorption time, the higher the desorption rate; however, an excessively long time will reduce the equipment utilization rate and increase production costs. 5.4.4 The desorption temperature must be strictly controlled to ensure uniform distribution at all points within the tower, in accordance with the regulations. 5.4.5 It is necessary to ensure that the composition of the desorption liquid meets the specified requirements. 5.4.6 Pay attention to the flow rate of the desorption liquid; it should generally be 1 to 5 volumes of carbon beds per hour. 5.4.7 Pay attention to the impurity content and pore characteristics of the gold-carrying carbon. Eliminating impurities within the carbon in advance (such as wood chips, plastic, coarse mineral sand, etc.) will help improve the desorption rate. 6. Regeneration of gold-removing carbon: The activity of activated carbon shows significant changes after adsorption, desorption, and regeneration. After acidic regeneration, the activity of gold-removing carbon does not increase significantly; only half of its original activity can be restored. Only through thermal regeneration is it possible to restore its activity to over 80%. The main reasons for the reduced adsorption activity of activated carbon are as follows: First, the pores of the carbon are blocked by inorganic substances; for example, quartz particles from slurry, clay sludge, and other such substances can easily be adsorbed by activated carbon and enter its pores, causing blockages. In addition, excessive amounts of ions from the slurry, as well as complexed ions of base metals such as copper, can also be adsorbed by the carbon particles, leading to the poisoning of the micropores and a decrease in their activity. Secondly, organic substances such as lubricants, detergents, flotation agents, and humic acids are all adsorbed by activated carbon, which greatly affects the activity of the carbon. Third, the degradation of active sites within activated carbon and the deformation of its pores are also reasons for the decrease in activity. Practice has shown that after acid treatment, the activity of gold-extracted carbon can be restored to 50–60, while after thermal regeneration its activity can be increased to over 85; in some cases it even exceeds the activity of new carbon. Acidity can be used: dilute hydrochloric acid or dilute nitric acid (concentration 1–5) can be employed at room temperature in specialized pickling tanks for a washing period of 2–4 hours, thereby removing compounds such as calcium and zinc from the carbon; whereas a hot acidic solution at 90–93°C can remove compounds of calcium, zinc, and nickel as well as most of the silicon. If the pores of the carbon are severely blocked by silicates, only an aqueous solution of hydrofluoric acid (HF) can be effective.