Chemical polishing of crystal glass with concentrated acids

The use of 40% HF, 92-94% H2SO4 and less concentrated acids for polishing crystal glass in Soviet plants is discussed. Use of more concentrated acids requires polishing schemes different from the existing one because the reduction in volume of acid needed to replenish the working solutions increases the accumulation of salts and the process becomes uneconomic. An apparatus is described which employs a system for preparing H2SO4 solutions used for polishing and washing. Spent solutions are allowed to settle for at least 24 h, after which the clear portion is passed to dispensers, while the sludge is drained for neutralisation or regeneration and re-use. In the dispensers, the purified solutions are replenished with highly concentrated acids, heated to a set temperature, and returned to the washed tanks. The demand for acids as well as neutralising agents is reduced by a factor of two.