Here in the states, the best way to dispose of Dichromate is to treat it with Potassium or Sodium Bisulfite or Metabisulfite. This will reduce the Hexavalent chrome to Trivalent chrome. The conversion is completed when the solution turns a brilliant emerald green.

If you are not allowed to flush this treated solution down the drain, you may neutralize it with a mild caustic solution which will cause the chrome to precipitate as chromium hydroxide. Chromium hydroxide is a common green pigment. Filter the green precipitate and throw it in the garbage.

Alan