Desorption Electrolysis System

Yantai Jinpeng Mining Machinery Co., Ltd.I. Basic Principle of Desorption and Electrolysis1.1 Principle of desorptionAfter the gold in cyanide solution is adsorbed by activated carbon, a reversible equilibrium state is established in the cyaniding system between the gold on the surface of gold-loaded carbon and the gold in cyanide solution. The gold-loaded carbon is also in the similar equilibrium state when it is desorbed. When adding CN- or OH- to the desorption system, as these anions are more easily adsorbed by the activated carbon, Au(CN-)2 already adsorbed will be recovered, and the reversible equilibrium of gold adsorption is interrupted and develops adversely against gold adsorption. This is gold desorption. The process of gold desorption is shown as follows:We can presume that desorption of gold from gold-loaded carbon is essentially trying to  destroy the equilibrium of activated carbon adsorption, and causing the process to develop adversely against gold adsorption. Therefore, increasing the cyanide density, increasing alkalinity, raising the temperature, boosting the pressure or adding organic solvent will accelerate desorption of gold from the activated carbon.1.2 Principle of electrolysisThe pregnant solution obtained through desorption of gold-loaded carbon contains gold undoubtedly. The gold contained in pregnant solution can be recovered by electrolytic method. Because no new substance is added into the solution in the process of electrolysis, pure gold sediments can be obtained, which facilitates the further treatment. Therefore, electrolytic method is adopted by most of the gold mines. Gold exists in the desorbed pregnant solution in the form of Au (CN-) 2. Precipitation of gold, silver and little copper is done by the cathode in the electrolysis process, and so it is with hydrogen due to water deoxidization. Oxygen is separated out by the anode, resulting in ionic oxidation, where carbon dioxide and nitrogen are separated. Here are the reactions: Other reactions also occur in the electrolysis process. However, these three kinds of reactions mentioned above are principal. Tests and research show that, under normal electrolytic conditions, main control procedures of gold electrolysis depends on the velocity of Au(CN)2¯ diffusing to cathode surface, and the gold deposition velocity is only subject to the control of mass transfer process. The electrolytic efficiency can be represented by the following formula: Log(CO/C1)=KmtS/2.3F Of which: Km=P/δ-----mass transfer coefficient; P----diffusion coefficient of discharging particle (Au(CN)2¯); δ----thickness of diffusion layer; CO----primary gold concentration; Ct----gold concentration after electrolysis; t----time of electrolysis; S----surface area of cathode  II. System Structure 2.1 System compositionThis system mainly consists of desorption part, electrolytic part, instrumental control part, pipeline, and valves. These parts are integrated with each other and form an integral system. Main equipment of this system includes desorption column, filter, electrolytic bath, circulating pump, electric heater, heat exchanger, stripping liquid storage tank, carbon storage tank, electric control cabinet, and rectification cabinet, etc. List of EquipmentDescriptionModelQ'tyDesorption columnJDJ07281FilterYM400×5501Electrolytic bathDJC16151Electric heaterJDDR-242Stripping liquid storage tankBJW10001Heat exchangerJDR04131Carbon storage tankCTC10001Liquid storage tankCYC15151 2.2 Technological flowHere is the technological flow chart:III. Operational Procedures 3.1 Formulating stripping liquidFormulation when the equipment pipeline is empty: Fill 1.0% sodium hydroxide and 0.1% sodium cyanide into stripping liquid storage tank; then, fill with water until the liquid level reaches overflow port. Start the agitator, and stop agitating until the liquid is dissolved completely. Formulation when there are some stripping liquid in the equipment pipeline: Fill in 1.0% sodium hydroxide and 0.1% sodium cyanide into stripping liquid storage tank; then, fill with water until the liquid level reaches overflow port. Start the agitator, and stop agitating until the liquid is dissolved completely. 3.2 Loading the carbonOpen the valve at the bottom of carbon storage tank and the liquid-inlet valve of desorption column, and fill water into the carbon storage tank, to flush the clean gold-loaded carbon into the desorption column. If the gold-loaded carbon is not clean, wash and clean them before loading. 3.3 Shutting down the system and discharging the liquidThere are two ways for the user's selection. Discharging completely: After shutting down all the electric devices, close the inlet valve of circulating pump, and open a bit the valve discharging to the storage tank of stripping liquid, to discharge the liquid in the system slowly. The discharging is finished when pressure indication of electrolytic bath is zero. Discharging partially: After shutting down all the electric devices, close the inlet valve of the filter and the inlet valve of desorption column, and open a bit the valve on the inlet pipeline of desorption column discharging to desorption tank, to discharge the liquid in the desorption column merely, and leave the other liquid in the system. If the stripping liquid should be replaced, discharge the liquid completely; if the user does not intend to replace the stripping liquid or prepares to take out the gold slime, discharge the liquid partially. 3.4 Discharging the carbonOpen the carbon-discharging valve at the bottom of desorption column and the air-inlet valve (carbon-loading valve) at the top of desorption column; start to discharge the carbon. In order to clean off the carbon and foreign matters stuck on the internal wall of desorption column, rinse it with water. Close all the valves and finish carbon discharging until only clean water comes out of the outlet of carbon-discharging pipe. 3.5 Taking out the gold slimeAfter discharging the liquid, open the electrolytic bath and take out the gold slime.  IV. Operation of the Equipment 4.1 Desorption columnDesorption column is used in the gold extraction by CIP process. Put the gold-loaded carbon into desorption column, to cause interaction with the medium - caustic soda solution fed in, which separates the gold from gold-loaded carbon and produces the precious fluid. Load the gold-loaded carbon into desorption column via the carbon inlet. The stripping liquid enters desorption column via the liquid inlet, to desorb the gold-loaded carbon. While the liquid in the column is rising slowly, the gold and other metals contained in the gold-loaded carbon are transferred into the liquid continuously, and are turned into desorbed pregnant solution . Under the action of continuous desorption, the gold-loaded carbon in desorption column are gradually turned into degolded barren carbon, which will be discharged from the carbon outlet after completion of desorption. In order to ensure the cleanliness of the internal wall, rinse the internal wall of desorption column with clean water after discharging the carbon each time, to prevent the caked mass from affecting normal operation. Here is the diagram of functions and configuration of the interfaces of desorption column:4.2 Electrolytic bathDJC1615 electrolytic bath consists of electrolytic bath body, cathode, and anode. Conduction electrodes made of pure copper are fixed on both sides of electrolytic bath. By connecting the conduction copper bolts with cathode and anode, electrolyze the desorbed pregnant solution  passing through the electrolytic bath under the condition of being energized, to make the gold deposit. The deposited gold slime is accumulated at the bottom of electrolytic bath. When the accumulated gold slime reaches a certain quantity, open the electrolytic bath to take out the gold slime. The desorbed pregnant solution is turned into the desorbed barren liquid after electrolysis. Up to 16 anodes and 15 cathodes can be installed on the electrolytic bath. The cathodes are welded with stainless steel plates to form a support frame. Carbon fiber felt is fixed on the support. For the strength of carbon fiber felt is low, please take care of it when installing and dismounting. Here is structural diagram of the electrolytic bath:4.3 Electric heaterThe electric heater is of a cylinder structure, equipped with 6 pieces of 4kW/380v tubular electric heating element. Gaskets are adopted for sealing the interior and exterior of the tubular electric heating element, and glands are used for pressing the interior and exterior tightly, and it is convenient to use the gland at the exterior for a tight pressing.Here is structural diagram of the electric heater:4.4 Storage tank for stripping liquidIt is of a cylinder structure, consisting of cylinder body and agitating unit, with agitating output of 1.5kW.Here is its structural diagram:4.5 Heat exchangerThe heat exchanger is of a cylinder structure, consisting of cylinder body, end plate cover and steel tube.Here is its structural diagram: