摘要 |
<p>The present invention relates to the field of industrial ecology. It deals with the process in which sludge, recovered in waste water treatment by hetero-coagulation is converted into red, redbrown pigment material. At first sludge is treated by phosphoric acid and afterwards by water-soluble zinc salt, and partly by zinc sulfate in the molecular ratio of Fe2O3 to ZnO as 1 to 0,1-0,3; the obtained mixture is homogenised, dried and thermally treated at the temperature of 800-850 oC.@</p> |