| 摘要 |
<p>PROBLEM TO BE SOLVED: To recover nickel as a reusable metal in a waste liquid at a low cost by adding an alkali to a nitric hydrofluoric acid pickling waste liquid to adjust the liquid to a specified pH range, removing the produced hydroxide precipitate, and adding sodium hydrogen boride to adjust the liquid to a specified pH range to crystallize and separate nickel. SOLUTION: An alkali is added to a nitric hydrofluoric acid pickling waste liquid to adjust the pH to 4.5 to 6.5 and the produced precipitate is removed. Then sodium hydrogen boride is added to the liquid to adjust the pH to 6.5 to 10.5. The concn. of calcium hydroxide used to adjust the pH to 4.5 to 6.5 is preferably 10 to 30 wt.%. In order to settle and separate fluorine as fluorides in the waste liquid, calcium salt such as calcium chloride is preferably added at the same time. The metal nickel precipitates in a slurry state are separated by filtering and dehydrated by using a filter press or the like. The filtrate and the supernatant are recycled in a factory. After the separated metal nickel precipitates are dried, they are used as metal nickel for the production of a stainless steel or the like.</p> |
