| 摘要 |
<p>PURPOSE:To concentrate process liquid of <=1pH of surface treatments for metals at a small energy cost without any special neutralization by treating said liquid with a polybenzimidazolone selective permeable membrane. CONSTITUTION:The above-described process liquid is subjected to a reverse osmosis treatment without neutralization with a polybenzimidazolone selective permeable membrane which has benzimidazolone rings and of which the selective permeability occurs mainly in the presence of said rings. For example, an object (a) to be treated which is carried into a bath tank A for surface treatment of metals through a pretreatment stage receives a surface treatment by treating liquid in said tank, after which it is immersed in a recovering tank B and is removed of the treating liquid stuck thereof; further, it is rinsed in rinsing tanks C, D. In this system, the recovering liquid is returned from the tank B into the tank A. At the same time, the treating liquid is partly removed from the tank A, and is concd. to about 1.1-1.5 times under about 20-70kg/ cm<2> pressures in a reverse osmosis device E. The concd. liquid is returned to the tank A, whereby the concn. of the tank A is maintained constant. The permeated liquid separated by the reverse oscmosis is fed to the tank B where it is reused as rinsing water for the object to be treated.</p> |
