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The following steps are used to prepare platinum nitrate:
(1) React platinum sponge with aqua regia to prepare a chloroplatinic acid solution. Add aqua regia to the platinum sponge in batches and heat appropriately, ensuring uniform bubbling during the reaction. After the reaction stops, add concentrated hydrochloric acid dropwise to the reaction solution of platinum sponge and aqua regia until no brown nitrogen oxides overflow from the reaction solution. Then add water to the reaction solution to remove the acid, filter to obtain the filtrate, and heat the filtrate to a mass-volume concentration of 100 g/L to obtain the chloroplatinic acid solution.
(2) React the chloroplatinic acid solution obtained in step (1) with oxalic acid solution to prepare a chloroplatinous acid solution. The amount of platinum chlorate solution and oxalic acid solution used is based on adding 0.64 g of oxalic acid per gram of platinum. The reaction temperature for chloroplatinic acid solution and oxalic acid solution is 50℃. A 10% oxalic acid solution is added dropwise to the platinum chloroate solution while stirring the reaction solution. After the addition is complete, the reaction solution is stirred for 1 hour. The reaction solution is heated until the volume is reduced by half to obtain chloroplatinic acid solution.
(3) The chloroplatinic acid solution obtained in step (2) is reacted with sodium hydroxide solution to prepare a platinum-containing precipitate. The amount of platinum chloroate solution and sodium hydroxide solution is 1.5 grams of sodium hydroxide per gram of platinum. The reaction between chloroplatinic acid solution and sodium hydroxide solution is carried out at 70℃. A 40% sodium hydroxide solution is added dropwise to the chloroplatinic acid solution while stirring the reaction solution. A black precipitate appears in the reaction solution. After the addition is complete, the reaction is continued for 2 hours. The reaction solution is filtered, and the precipitate is washed with deionized water until the washing solution is free of chloride ions. The precipitate obtained is the platinum-containing precipitate. (4) Platinum nitrate was prepared by reacting the platinum-containing precipitate obtained in step (3) with concentrated nitric acid, wherein 10 mL of concentrated nitric acid was added for every gram of platinum. The reaction between the platinum-containing precipitate and concentrated nitric acid was carried out at 70 °C. Concentrated nitric acid was added to the platinum-containing precipitate and reacted for 15 hours under stirring. The reaction solution was cooled and filtered to obtain a platinum nitrate solution. The platinum nitrate solution was heated until a solid crystalline film appeared, and then dried under vacuum at 50 °C to obtain dark brown platinum nitrate.