Gold can only be dissolved in aqua regia and alkali metal cyanide solution under normal conditions. Therefore, the gold-containing waste liquid produced in the industry mainly includes gold waste king aqueous solution and gold cyanide waste liquid. 1. Gold-containing waste Wangshui Dissolving gold-containing solid waste in aqua regia is the most commonly used method for transferring gold into solution. The resulting solution has a large acidity, often referred to as gold-containing waste aqua regia, in which gold is present in a +3 oxidation state. The basic principle for recovering gold from this is to supply electrons to these free or coordinated gold ions, which are converted into atomic states to obtain gold. There are two common methods for supplying electrons to gold ions: one is to add a suitable reducing agent to the aqueous solution of the waste king to reduce the gold ions; the other is to provide electrons to the gold ions by electrolysis to precipitate gold at the cathode. Currently applied industrially and in reducing waste for recovery of gold in aqua regia mainly ferrous sulfate, sodium sulfite, active transition metals (such as zinc powder and iron powder), sodium bisulfite (NaHSO 3), oxalic acid, formic And hydrazine, etc. When recovering gold using the reduction method, attention must be paid to the acidity and oxidative strength of the waste aqua regia. In general, waste aqua regia is very acidic and oxidizing, and it is necessary to try to reduce its acidity and oxidizing properties before adding a reducing agent. The commonly used method is to filter the gold-containing waste aqua regia to remove insoluble impurities, and the obtained filtrate is placed in a porcelain or glass-lined container to be heated and boiled, and a certain amount of hydrochloric acid is added dropwise in a small amount in the process to make waste. Nitrogen oxide gas in the aqua regia escapes. This operation is commonly known as catching nitrate. The simple criterion for whether or not the nitrate is completely eliminated is that the color of the gas escaping from the waste king water must be colorless. Ferrous sulfate is a cheap and inexpensive inorganic reducing agent for industrial use. Its redox reaction with waste aqua regia is as follows: 3FeSO 4 +HAuCl 4 HCI→FeCl 3 +Fe 2 (SO 4 ) 3 +Au↓ The gold-containing waste aqua regia which has been filtered and washed with water is sucked into a high-position tank, and is added dropwise to an excess saturated ferrous sulfate solution under stirring, and the ferrous sulfate solution can be appropriately heated. When a small amount of 0.1 mol/L HAuCl 4 solution was added dropwise to the reaction mixture of a small amount of ferrous sulfate, there was no significant reaction, and it was considered that the reaction mixture was not reduced. Stop adding waste aqua regia and continue stirring for 2 hours, then let stand to settle. The precipitated black gold powder was separated by a tilting method, washed with water and then cast to obtain a crude gold. The filtrate obtained was concentrated and further treated with zinc powder. Because of the small reduction ability of ferrous sulfate, it is difficult to reduce the metal other than precious metal when it is treated with ferrous sulfate. Therefore, even if it is treated with gold-containing waste liquid containing more ruthenium metal, it is reduced. The grade of gold can also reach over 98%. However, this method is slow, the end point is not easy to judge and the gold is not easily completely reduced, so the zinc powder is still needed to further treat the tail liquid. Sodium sulfite is also an inexpensive reducing agent commonly used in industry. Many smelting companies usually introduce the dust after flue gas into the sodium hydroxide solution in order to reduce the sulfur dioxide content in the soot when roasting sulfur-containing minerals or other materials. The content of sodium sulfite is relatively high, and this solution can be directly used as a reducing agent for treating gold-containing waste aqua regia to achieve the purpose of waste treatment and comprehensive utilization. The same effect can be achieved by directly passing the dust-removed and purified sulfur dioxide-containing gas into the gold-containing waste aqua regia. The reaction equation for the reduction of gold-containing waste aqua regia by sodium sulfite is as follows: Na 2 SO 3 +2HCl→SO 2 +2NaCl+H 2 O 2SO 2 +2HAuCl 4 +6H 2 O→2Au↓+8HCl+3H 2 SO 4 The specific operation is as follows: the gold-containing waste Wangshui filtered and leached into the high-temperature tank is added to the excess saturated sodium sulfite solution under stirring, and the solution is heated appropriately during the reduction, which is favorable for producing the large-particle yellow sponge. gold. A small amount of polyvinyl alcohol (addition amount of about 0.3 to 30 g / L) is added as a coagulant to facilitate the sedimentation of the floating gold powder, and the reaction is allowed to stand after the reaction. The precipitated black gold powder was separated by decantation, washed with water and then cast to obtain crude gold. Zinc powder is a metal reducing agent commonly used in gold refining process. It is characterized by large reduction capacity and fast replacement of gold. The disadvantage is that the excess zinc powder is mixed with the gold powder obtained by the replacement, and the excess zinc powder must be dissolved again with nitric acid or hydrochloric acid to obtain a relatively pure gold powder. The gold-containing waste Wangshui, which has been filtered and sifted, is pumped into the high tank, and the pH of the solution is adjusted to 1 to 2, and excess zinc powder is added. After sufficient reaction, the mixture was centrifuged, and the resulting gold-zinc mixture was repeatedly washed with deionized water until no chloride ions were present. The mixture was boiled with nitric acid under stirring, and the color of the obtained gold powder was normal golden yellow, and the agglomeration was good. After washing with water, the ingot was obtained into a crude gold. The purpose of controlling pH=1~2 during the replacement process is mainly to prevent hydrolysis of zinc salts, which is beneficial to product clarification and filtration. The metal precipitate produced by the displacement contains an excess of zinc powder which can be dissolved with nitric acid or hydrochloric acid. It should be noted that when dissolved in hydrochloric acid, the precipitate should not contain nitrate. Except silver , lead and mercury , the other base metals are easily dissolved by hydrochloric acid. When nitric acid is used for dissolution, nitric acid can dissolve almost all common metal impurities contained in the gold powder, but the precipitate should not contain chloride ions, otherwise the gold powder obtained by the reduction may be dissolved again. In addition, sulfuric acid can also be used to dissolve zinc and other impurities, and the precipitated gold is not easily re-dissolved, but the calcium and lead ions cannot be separated from the precipitate, and the product tends to be black. For waste aqua regia with a very low gold content and a large amount of gold, the energy consumption is too high when the nitrate treatment is carried out. It can be reduced by using sodium hydrogen sulfite (NaHSO 4 ) as a reducing agent, and it is not necessary to use sodium hydrogen sulfite for reduction. . The specific operation is: after filtering the gold-containing waste aqua regia, first adjust the gold-containing waste aqua regia with a solution of an alkali metal or an alkaline earth metal hydroxide (for example, a NaOH or KOH having a mass of 25% to 60%) or a carbonate solution. The pH was 2 to 4, and it was heated to 50 ° C for a while, and a small amount of butyl stearate was added as a coagulant. Gold was precipitated by dropwise addition of a saturated solution of NaHSO4 under stirring. The obtained gold powder can be melt-cast into coarse gold after washing, and the content is about 98%. The most important benefit of using gold oxalic acid, formic acid, ascorbic acid and hydrazine hydrate to reduce the gold-containing waste aqua regia is that no new impurities will be introduced, but the cost is high, and it is rarely used when recovering gold powder from gold-containing waste aqua regia. It is used more when processing electrolytic gold into a gold powder industrial product of a specific particle size. Whether the tailings of various reducing agents still contain gold, that is, whether the recovery is complete, the following method can be used for judging: according to the color of the tail liquid, if the tail liquid is colorless, the gold has been basically precipitated and extracted completely; The stannous acid solution is checked. When gold is present, the colloidal fine gold is suspended in the solution to make the solution purple-red; otherwise, the gold in the tail liquid has been completely extracted. 2. The second major category of gold-containing cyanide waste liquid is gold-containing cyanide waste liquid, which mainly includes gold-plated waste liquid produced by electroplating process (general acid gold-plated waste liquid contains gold 4~12g/L, medium-acid gold plating) The waste liquid contains 4g/L of gold, the alkaline waste liquid contains 20g/L of gold, the waste water produced by the cyanidation process, and the waste water produced by the production process of gold-containing cyanide products (such as potassium cyanide). The gold recovery methods commonly used in gold-containing cyanide wastewater mainly include electrolysis, displacement and adsorption. According to the type of gold-containing cyanide wastewater and the gold content, a single method can be selected, or several methods can be combined. 1 Electrolytic method: The gold-containing cyanide wastewater is placed in an open-type electrolytic cell, with stainless steel as the anode and pure gold flakes as the cathode. The control liquid temperature is 70-90 ° C, and the electrolysis is carried out by direct current, and the cell voltage is about 5-6 V. . Under the action of direct current, gold ions migrate to the cathode and deposit and precipitate on the cathode. When the plating solution in the tank is subjected to timed sampling analysis and the gold content falls below the specified concentration, the electrolysis is terminated, and then the new spent plating solution is replaced by electroplating. When the cathode precipitated gold accumulated to a certain amount, the cathode was taken out, and after washing, it was cast into a gold ingot. The electrolytic treatment of gold-containing cyanide wastewater can be treated by closed-cell electrolysis in addition to the above-mentioned slotted electrolysis. That is, a closed electrolytic cell is used for the electrolysis operation, the solution is circulated in the system, and the control cell voltage is 2.5 V for electrolysis. When the gold content of the waste plating solution is lower than the specified concentration, the electrolysis is stopped, and then the tank is drained, washed, and ingot is cast. After the electrolytic tail liquid is treated to the standard by the absorption tank, it is discarded. Closed-cell electrolysis has a higher degree of automation and is more environmentally friendly, but the one-time equipment investment is larger. 2 Replacement Gold in gold-containing cyanide wastewater is usually present in the form of [Au(CN) 2 ]-. The gold in [Au(CN) 2 ]- can be reduced by adding a suitable reducing agent to the gold-containing cyanide wastewater. According to the type and gold content of the gold-containing cyanide wastewater, the reducing agent may be an inorganic reducing agent (such as zinc powder, iron powder, ferrous sulfate, etc.) or an organic reducing agent (such as oxalic acid, hydrazine hydrate, ascorbic acid, formaldehyde, etc.). Inorganic reducing agents are less expensive than organic reducing agents, but after treatment of gold-containing cyanide wastewater, excess inorganic reducing agent must be removed. The organic reducing agent is expensive, but the product after the reduction of the gold cyanide complex is easily separated from the gold. Since gold is first obtained in the recycling process, the latter purification is inevitable. Therefore, in the actual operation, inorganic reducing agents (especially zinc powder and iron powder) are generally used for reduction, and gold is replaced by black gold powder to sink the bottom of the tank. The reaction equation for zinc powder reduction is as follows: 2KAu(CN) 2 +Zn→K 2 Zn(CN) 4 +2Au↓ The specific operation steps are as follows: sampling and analyzing the gold-containing cyanide wastewater to determine the gold content therein. The waste liquid was placed in a plastic container, and about 1.5 times the theoretical amount of zinc powder was added and stirred. In order to speed up the replacement process, the gold-containing waste plating solution should be appropriately diluted and acidified to control pH=1~2. HCN gas is easily released when acidifying waste liquid, so the work should be carried out in a fume hood. After the displacement product is filtered, it is immersed in sulfuric acid to remove excess zinc powder, and then washed, dried, and cast to obtain crude gold. The filtrate is analyzed for gold content and free cyanide content. When the gold content and free cyanide content are lower than the specified value, it can be discharged; otherwise, it should be further processed. 3 Activated carbon adsorption activated carbon has a high adsorption capacity for gold cyanide complexes. The adsorption process of activated carbon includes adsorption, desorption, backwash regeneration of activated carbon and gold extraction from the backwash. After the gold-containing cyanide wastewater is tested for gold content, it is placed in a plastic container. Add activated carbon of appropriate particle size and stir well. The adsorbed mixture was centrifugally dehydrated, and the resulting liquid was collected and concentrated. The obtained wet solid was added to a mixed solution composed of 10% NaCN and 1% NaOH, heated to 80 ° C, and desorbed with sufficient stirring. Filtration or centrifugal dehydration, the obtained filtrate is a gold-containing backwashing liquid, the activated carbon is added to deionized water, stirred well, dehydrated, and repeated three times. The obtained filtrate is contained in a gold backwashing liquid, and the activated carbon can be reused after being dried. The amount of gold in the backwash has been greatly improved. The gold in the backwashing liquid can be extracted by electrolysis or reduction. When the gold-containing cyanide wastewater is treated with activated carbon, the adsorption of [Au(CN) 2 ]- by activated carbon in the waste liquid is generally considered to be a physical adsorption process. The size of the activated carbon porosity directly affects the size of its activity. The stronger the activity of carbon, the greater the adsorption capacity of gold. Commonly used activated carbon has a particle size of 10 to 20 mesh and 20 to 40 mesh. The adsorption capacity of activated carbon for gold can reach 29.74g/kg, and the adsorption rate of gold is 97%. The South African patent believes that the treatment of waste cyanide solution with ozone, air or oxygen, and then adsorption with activated carbon can achieve better results. Further, the desorbent may be selected from water-soluble alcohols and aqueous solutions thereof, and ketones soluble in strong bases and aqueous solutions thereof may also be used. The composition (volume percent) of such desorbents is: H 2 O (0-60%), CH 3 OH or CH 3 CH 2 OH (40% to 100%), NaOH (≥0.11 g/L); or CH 3 OH (75% to 100%), water (0 to 25%), NaOH (20.1 g/L). 4 Ion conversion method Because gold in the gold-containing cyanide wastewater exists in the form of [Au(CN) 2 ] anion, an appropriate anion exchange resin can be used to ion-exchange gold from the gold-containing waste liquid, and then use a suitable solution. Au(CN) 2 ] an anion is extracted from the resin. The anion exchange resin is packed into a column, and the flow rate of the column is first tested with deionized water. After the adjustment, the filtered gold-containing waste liquid is passed through an ion exchange column to periodically detect the gold content of the effluent. When the gold content of the effluent exceeds the specified standard, the discharge of gold-containing cyanide wastewater is stopped. The gold is repeatedly eluted with a thiourea hydrochloric acid solution or an acetone hydrochloric acid solution to regenerate the resin. The gold content of the eluent is greatly increased, and the gold in the eluate is extracted by electrolysis or reduction. 5 The basic principle of the solvent extraction method is to extract the gold-containing complex into the organic phase for enrichment by using the gold cyanide complex in the gold cyanide-containing wastewater in a certain organic solvent to have a solubility greater than that in the aqueous phase. The organic phase is treated to obtain a crude gold. Tests showed that the organic solvent used for extraction of gold can be many, such as tributyl ethyl acetate, an ether, dibutyl carbitol, methyl isobutyl ketone (of MIBK), phosphate (TBP), tri-n-octyl Both phosphine oxide (TOPO) and trioctylmethylamine salts can extract gold from a gold-containing solution. During the extraction operation, the extraction route of the gold-containing waste liquid is generally controlled at 3 to 8 times. If the extraction agent is properly selected, the extraction recovery rate can generally reach 95% or more. Weight Chromium Potassium method (of CODCr in) Overview First, the principle In the strongly acidic solution, a certain amount of potassium dichromate oxidizes the reducing substance in the water sample, and the excess potassium dichromate is used as an indicator of the test ferrous iron and is returned by the ammonium ferrous sulfate solution. The oxygen consumed by the reducing substance in the water sample is calculated based on the amount. Second, interference and its elimination Acidic potassium dichromate is highly oxidizing and can oxidize most organic substances. When silver sulfate is used as a catalyst, linear aliphatic compounds can be completely oxidized, while aromatic organic compounds are not easily oxidized, pyridine is not oxidized, and volatility is straight. An organic substance such as a chain aliphatic compound or benzene exists in the vapor phase, and cannot be in contact with the oxidant liquid, and the oxidation is not remarkable. Chloride ions can be oxidized by dichromate and can react with silver sulfate to cause precipitation, which affects the measurement results. Therefore, mercury sulfate is added to the water sample before reflux to become a complex to eliminate interference. Samples with a chloride ion content higher than 2000 mg/L should be diluted first, and the content should be reduced to 2000 mg/L, and then measured. Third, the scope of application of the law The COD value of more than 50 mg/L can be determined by using a potassium dichromate solution at a concentration of 0.25 mol/L. The COD value of 5-50 mg/L can be determined by using a potassium dichromate solution at a concentration of 0.25 mol/L, but the accuracy is poor. instrument 1. Reflow device: All-glass reflow device with a 250ml Erlenmeyer flask (for example, an all-glass reflow device with a 500ml conical flask with a sample volume of 30ml or more). 2. Heating device: electric heating plate or variable group electric furnace. 3, 50ml acid titrant. Reagent 1. Potassium dichromate standard solution (1/6=0.2500mol/L:) Weigh the standard or superior pure potassium dichromate 12.258g which was pre-baked at 120 °C for 2h, dissolved in water, transferred to 1000ml volumetric flask, diluted Go to the marking line and shake well. 2. Test the ferrous iron indicator solution: Weigh 1.485 g of phenanthroline, 0.695 g of ferrous sulfate dissolved in water, dilute to 100 ml, and store in a brown bottle. 3. Ammonium ferrous sulfate standard solution: Weigh 39.5g of ammonium ferrous sulfate dissolved in water, slowly add 20ml of concentrated sulfuric acid while stirring, transfer to 1000ml volumetric flask after cooling, dilute to the mark with water, shake. Before use, calibrate with potassium dichromate standard solution. Calibration method: Accurately measure 10.00ml potassium dichromate standard solution and 500ml conical flask in West Bank, dilute to 110ml with water, slowly add 30ml concentrated sulfuric acid, and mix. After cooling, three drops of the test thief indicator solution (about 0.15 ml) were added and titrated with ammonium ferrous sulfate. The color of the solution was from yellowish green to reddish brown and the end point. Wherein c-concentration of ammonium ferrous sulfate standard solution (mol / L); V - the amount of ammonium ferrous sulfate standard titration solution (ml). 4. Sulfuric acid-silver sulfate solution: 25 g of silver sulfate was added to 2500 ml of concentrated sulfuric acid. Place for 1 to 2 days, shake it from time to time to dissolve (if there is no 2500ml container, 5g silver sulfate can be added to 500ml concentrated sulfuric acid). 5. Mercury sulfate: crystal or powder. Precision and accuracy Six laboratories analyzed a standard solution of 150 mg/L of potassium hydrogen phthalate, with a relative standard deviation of 4.3% in the laboratory; the relative standard deviation between laboratories was 5.3%. Precautions 1. The maximum amount of chloride ion complexed with 0.4g of mercury sulphate can reach 40mL. For example, take 20.00mL water sample, that is, the water sample with the highest concentration of 2000mg/L chloride ion. If the chloride ion concentration is low, it is also possible to add less mercury sulphate to maintain mercury sulphate: chloride ion = 10:1 (W/W). If a small amount of mercury chloride precipitates, it does not affect the determination. 2. The volume of water sample can be between 10.00 and 50.00mL, but the reagent dosage and concentration can be adjusted accordingly, and satisfactory results can be obtained. 3. For water samples with a chemical oxygen demand of less than 50 mol/L, it should be 0.0250 mol/L potassium dichromate standard solution. A 0.01/L ammonium ferrous sulfate standard solution was used for the back drop. 4. After the water sample is heated and refluxed, the remaining amount of potassium dichromate in the solution should be 1/5 to 4/5 of a small amount. 5. When the quality and operation technique of the reagent is detected by the potassium hydrogen dibasic acid standard solution, since the theoretical CODCr per gram of potassium hydrogen dibasate is 1.167 g, 0.4251 L of potassium hydrogen phthalate and red distilled water are dissolved. Transfer to a 1000 mL volumetric flask and dilute to the mark with heavy distilled water to make a 500 mg/L CODCr standard solution. New with time. 6. The CODCr measurement results should retain three significant figures. 7. For each experiment, the standard titration solution of ammonium ferrous sulfate should be calibrated. Pay attention to the change of concentration when the room temperature is high. Chemical Storage Tank is used to storage different liquid, like oil, fuel, gasoline, petrol, coolant. 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