명반석을 황산으로 처리한 추출용액에 황산암모늄을 가하면 용존알루미늄성분이 명반결정으로 회수되며 광적내에 존재하였던 철성분은 용액내에 잔류하여 분리된다. 이때 황산암모늄을 광잉 첨가하면 위와 같이 만들어진 명반의 용해도가 더욱 감소되는 이점이 있다. 이러한 방법으로 알루미늄성분을 회수하였을 때 경제적인 회수조건은 황산암모늄의 첨가량을 추출용액에서 명반결정을 여과한 뒤 여액내의 황산암모늄 농도가 10 %함유하도록 조절하여 넣고 추출액을 가열, 10 ℃로 냉각하여 명반결정을 얻은 경우이었으며 이때 명반의 회수율은 97 %, 철분의 제거율도 97 %에 도달하였다.

The dissolved aluminium component extracted from alunite ore by sulfuric acid could be recovered as alum crystal by the addition of ammonium sulfate into the extracted solution, in which the iron component being separated from the one still dissolved. Addition of ammonium sulfate in excess appeared profitable through it decreasing the solubility of alum once formed. The economic recovery of the dissolved aluminium was accomplished when the excess amount of ammonium sulfate addition was adjusted such that the concentration of the unreacted ammonium sulfate remaining in the filtrate would be about 10 %. Heating the extracted solution was necessary after the addition of ammonium sulfate as crystal to dissolve the latter, and in the ensuing step the solution was cooled down to 10 ℃ to crystallize the alum. In such a procedure 97 % of the dissolved alum was recovered, also 97 % of the iron component being left in the solution separated from the aluminium component.