The solubility product of Tin sulfide (SnS2) is very small, about 2.5 × 10-27. Thus, under the certain conditions, adding a sufficient amount of sulfide ions into tin-containing solution can remove most of the tin as sulfide precipitate.

 

The main operating conditions : adjust the pH to 9 to 11 during the crude tungsten acid solution purification removing phosphorus, arsenic, silicon, making the most of the tin hydrolysis; then add the theoretical amount of 30% to 50% of sodium sulfide, so that tin hydroxide formed by the reaction of tin sulfide precipitation, prompting hydrolysis proceed. Plus magnesium and phosphorus purification, arsenic, silicon, and then when the theoretical amount of acid added 150% to 200% of sodium sulfide (adjusted to weakly acidic acid) to remove the solution remaining in the tin.

 

In the first stage of detinning process, the theoretical amount of sodium sulfide was added 30 to 50, because if excessive amount of sodium sulfide, tin sulfide generated precipitate will dissolve in excess sodium sulfide, the resulting thio tin ions (SnS32 -), but not reach except tin effect: SnS2 + S2 - SnS32-

 

In the second stage of detinning process needs to adjust the acid because the theoretical amount of 150% to 200% sodium sulfide must be added when the depth detinning. In order to prevent re-tin sulfide precipitate was dissolved in an excess of sodium sulfide, the pH was adjusted to weakly acidic solution shall, tin sulfide stable. Because tin sulfide is insoluble in dilute acid, and an excess of sodium sulfide reacts with the acid toxic H2S gas evaporate.