METHOD FOR SELECTIVELY RECOVERING SALT COMPONENT FROM WASTE SALT CONTAINING NITRATE, NITRITE AND HYDROXIDE GENERATED DURING HEAT TREATMENT OF STEEL PART IN SALT BATH

摘要

PROBLEM TO BE SOLVED: To provide a simple method for selectively recovering salt components and capable of obtaining directly usable salts in high yield from waste salts containing nitrates, nitrites and hydroxides generated during a heat treatment of steel parts in a salt bath by carrying out a specific means. SOLUTION: The subject method is to dissolve waste salts in water, separate insoluble residues and fractionally crystallize alkali nitrates. The solid waste salt is crushed to 1-50mm granule size and dissolved in a solution containing hydrogen peroxide acidified by nitric acid at 40-90 deg.C. Insoluble residues are filtered and the concentrated solution is neutralized and cooled to -10-+20 deg.C to precipitate potassium nitrate. The solution is concentrated at 60-120 deg.C to crystallize sodium chloride. Sodium nitrate is crystallized by adding concentrated nitric acid to the residual solution. Advantageously barium possibly present in a weak alkaline medium is precipitated and separated as barium carbonate by adding carbonate and an alkali after dissolving the waste salts.