Abstract
The kaolinite suspension containing water glass is the one of the most popular waste water from chemical grouting tunnel constructions. In this study treatability of kaolinite suspension containing water glass in the coagulation process has been investigated. To make clear the effects of soluble or polymerized silicate on the coagulation process, various experiments were carried out. The polymerization rate and the value of electric charge of colloidal silica were measured under various pH and initial soluble silicate concentrations to characterize the nature of silicate.
The results obtained by the study can be summarized as follows.
(1) The highest polymerization rate of silicate is observed at pH 8.5 under the concentration of 300-1500 mg/l.
(2) Polymerized silica colloids show the largest negative charge at pH 9.2-9.5.
(3) The optimum pH range for the coagulation of kaolinite coexisting with water glass is between 4.5 and 7.0. The optimum pH value, however, changes depending upon the concentration of the soluble silicate and alum (aluminium sulfate) dosage.
(4) In the above mentioned optimum coagulation pH region, silicate exists mainly as the monomer. Therefore, polymerized silica dose not play an important roll for coagulation.
(5) Removal of soluble silica is very difficult by the both reasons that it requires high alum dosage and generates high sediment volume.
