Abstract
Recently, huge amount of waste has been recycled in cement plant, and many kinds of aversive substances (chlorides, alkalies, sulfates and heavy metal salt) have been brought into cement manufacturing process with the wastes as raw materials. These substances are usually removed by chlorine bypass system from cement kiln-preheater, called as “K powder”. Since cement plant is expected to use more wastes, “K powder” constituents should be separated with each other as recycled resources.
In this study, we tried sulfidized flotation to separate lead components from “K powder” with the recovery of more than 60% by optimizing the flotation conditions, and clarify the reaction mechanism. As a result, we found the optimum conditions in case of 150 g/L pulp density of “K powder” as follows. 1) Adjust the initial pH of the pulp to 3.0 by sulfuric acid, 2) Take 30 min for aging of gypsum formation at the pH 3.0, 3) Add the NaHS of 20 g/kg-“K powder” and take 15 min for sulfidization, 4) Add the PAX of 3.2 g/kg-“K powder” and take 15 min for conditioning, 5) Readjust the pH to 3.0∼4.0 by sulfuric acid and carry out flotation. We also found that the formation of K2Pb(SO4)2 during the conditioning causes the decrease of lead recovery in flotation and that the K2Pb(SO4)2 formation can be suppressed by limiting K+ concentration in solution under 800 mmol/L and/or keeping the pulp temperature over 40°C at the stage of NaHS addition. Then, we could separate lead components from “K powder” with the recovery of 60 % as a lead concentration of 10∼30 Pb wt% under the same condition of sulfidized flotation for the “K powders” of various component.
