抄録
Pressure flotation experiments of metallic hydroxides were carried out without using any collectors in order to obtain fundamental data for elucidating the flotation mechanism.
When the solutions containing 1×10-3 to 5×10-3 mole/l of metallic ions, such as Cu2+, Zn2+ and Fe3+ ions, were used as sample solutions and the pH values were adjusted with NaOH or Ca (OH) 2, metallic hydroxides precipitated were effectively floated. But, the flotation removal of metallic hydroxides decreased remarkably, as the initial concentration of metallic ions decreased to less than 1×10-3 mole/l.
Ferric hydroxides precipitated with CaCO3 from ferric sulfate solution could not be floated. These ferric hydroxides have good settling characteristics, the reason of which has been considered to be due to the cutting of their gelatiniform structure with gypsum formed on the surfaces of CaCO3 particles. It was concluded, from the above experimental results, that the gelatiniform structure plays an important role which allows the trapping of gas bubbles in it in the pressure floatation of metallic hydroxides.
Cd2+ ions in waste waters are generally dilute in concentration and the solubility of cadmium hydroxides is large. However, the flotation removal of Cd2+ ions could be easily achieved by coprecipitating them with ferric hydroxides at comparatively low pH values.
Finally, the results of the pressure flotation of ferric hydroxides, which were precipitated by adding Ca (OH) 2 to ferric sulfate solution, were compared with those of the settling. It was found that the pressure flotation could be operated in a shorter time than the settling. The residual ferric ion concentration and the sludge volume were the same in both methods.
