| 摘要 |
<p>A paste of the discoloured minerals e.g. kaolin, clays, barytes, glass-silica, which is stable to acids, is mixed with H2HSO4 to pH 5 - 7 and placed in an enclosed reator. Finely divided Zn and excess SO2 (to that for ZnS2O4) are introduced and the treatment effected in the absence of O2, while maintaining pH is not >4. Zn is used as not >0.1 wt. % (w.r.t. dry mineral) and a wt. ratio Zn : SO2 of 1 : 3 - 8. Slightly improved whitness is obtained than with prior methods, using considerably less reductant.</p> |
