Other methods for recovering silver from the fixer are: 1. Sodium borohydride reduction method The trade name of sodium borohydride is SBH. It can be used from a reduction of gold and silver acidic or alkaline fixing solution, cyanide solution, chloride solution and the precipitated silver chloride, it is also from reduction of platinum and palladium. Its reduction reaction is: 8M n + +NaBH 4 +2H 2 O For example, there are two kinds of sodium borohydride produced by Morton Vulcanized Rubber Company of the United States, one is a powder or tablet containing 98% of NaBH 4 , and the other is a liquid containing 12% of NaBH 4 and 40% of NaOH. The latter is low in price and is more convenient for reduction under alkaline conditions. There is also a DMAB which is a derivative of NaBH 4 , dimethane borane [(CH 3 ) 2 HN·BH 3 ], which also has a similar reduction. When these products are used, their reduction depends on the BH 4 - content therein. According to the above reaction formula, the theoretical consumption (g) of NaBH 4 required to reduce each gram of precious metal can be calculated from the relative atomic mass and chemical price of the metal: Reduction metal amount ∕g Au + Ag + Pt 4 + Pd 2 + Ir 4 + Rh 3 + NaBH 4 theoretical quantity / g 0.0245 0.0447 0.099 0.0908 0.100 0.141 In practical applications, the amount used in the alkaline solution is about 1.1 times the theoretical amount, and in the acidic solution is about 2.0 times the theoretical amount. If the solution contains an oxidizing agent, such as a color plate fixing solution containing Fe 3 + , it will consume NaBH 4 and be reduced to Fe 2 + , so the silver is reduced from the color plate fixing solution, and the NaBH 4 consumption is more than that in the black and white plate fixing solution. The reduction operation is carried out according to the silver content in the fixing solution, and slowly added (10 to 20 minutes after completion) with stirring, the amount of NaBH 4 diluted with water is required, and gray black particles of silver are generated in the solution and hydrogen is evolved. After the reaction is completed, it is allowed to stand for a while to completely precipitate the silver particles, and then the supernatant is decanted, followed by filtration and drying. If the silver in the test solution has been completely reduced, a few drops of NaBH 4 solution can be added to the supernatant. If no gray-black precipitate appears, the reaction end point is reached. According to the acidity and alkalinity of the fixing solution, add NaOH or acetic acid to adjust the pH=5.5, slowly add 5-10 times of NaBH 4 solution with water under strong stirring, continue stirring for 30-40 minutes after 30 min addition, and wait for the silver precipitate after standing. The supernatant is withdrawn, and the silver powder is filtered, washed with water, dried, and then fluxed to melt the ingot. The recovery rate of silver is more than 99%, the residual liquid contains silver to 10 mg/L, the precipitated silver grade is 96% to 98%, and the grade of the smelted ingot can be increased to 99%. When sodium hydroxide is added to the fixing solution to adjust the pH to 6-8, the addition of 22 kg of silver per kg of NaBH 4 can be calculated. After the silver reduction precipitation, the residual NaBH 4 in the solution does not affect the return of the fixing solution. Second, the ion adsorption method The silver is adsorbed from the waste fixing solution by using an alkaline solution of an intermediate product viscose waste-fiber xanthogen which produces chemical fiber, and the solution contains silver 2.84 g ∕L, pH 7, and the viscosity: fixing solution = 1:10 At room temperature, static adsorption for 24h, silver adsorption recovery rate of up to 100%. Tests have shown that the degree of esterification of sodium cellulose xanthate has no effect on the adsorption of silver. However, the pH of the fixer has a great influence on the adsorption rate of silver. For example, when the pH is 6, the adsorption rate drops to 82%; when the pH is 9, a gelatinous precipitate that is difficult to filter is formed. From the cellulose-containing fiber, 93% to 99% of silver can be recovered from the alkaline fixing solution. Under neutral and acidic conditions, the adsorption recovery of silver was 25% and 88%, respectively. The silver-adsorbed fiber was incinerated at 300 to 500 ° C to obtain ash containing 21% of silver. The use of zinc sulfide-containing particles (such as copper sulfide or water-insoluble substance) cellulosic fibers, the silver can be recovered selectively from the solution of different chemical composition. Even if the solution contains very poor silver, a high recovery rate can be obtained. When used to recover silver from a fixer, the cost is only 10% to 12% of the value of the recovered silver. Using a strong basic anion exchange resin, 91.7% of the silver in the fixing solution can be recovered. The silver in the fixing solution can be precipitated using an organic compound containing an S or N functional group. For example, take 5L of fixer solution containing 3.2g ∕L X-ray film automatic processor, add 5% NaOH solution to adjust pH to 7, add 75mL of ALM-648 (Nippon Soda KK) solution to the solution, stir for 3min and filter. A precipitate of 50 g was obtained. The silver content of the filtrate can be reduced to 0.72×10 -6 , and the recovery of silver in the precipitate is greater than 99.99%. Wear Resistant Steel,Wear Resistant Plate For Industry,Wear Resistant Steel Plate For Industry Henan Houming Industry Co., Ltd. , https://www.houmingsteel.com
8M+NaBO 2 +4H 2 ↑