to 10 mm it has been found that following comminution to a particle size of from 1 to 50 mm advantageously from 5 to 10 mm of the solid used hardening shop salts which contain nitrite nitrate hydroxide the salt constituents are dissolved completely by leaching in a starting mixture containing nitric acid and hydrogen peroxide this process simultaneously oxidizes the nitrite ions to nitrate and neutralizes carbonate and hydroxide with the formation of nitrate salts as a result of the presence of hydrogen peroxide in the starting mixture contrary to expectations when the nitrite salt is introduced in the form of coarse granules as it contacts the starting mixture containing nitric acid no no x gas is given off this result is explained by the relatively small reaction surface area and the instantaneous further reaction between no x gases arising in the solution and the hydrogen peroxide this combination of reagents in the solution furthermore ensures that cyanide containing salt which may be incorrectly marked is detoxified by reaction with the nitrite and the hydrogen peroxide without causing problems the process can be controlled by monitoring the ph and measuring the redox potential a further advantage is that the reaction heat liberated by the oxidation and neutralization offsets the endothermic dissolution process as a result a solution temperature of from 50 u00b0 to 80 u00b0 c is adjusted which enables a very high salt concentration to be achieved thus between 100 and 200 kg nitrate containing used salt can be dissolved in a.