Foam Separation Processes from
Industrial Waste Treatment: Phenol,
Phosphate, and Hexavalent Chromium
ROBERT B. GRIEVES, Associate Professor
Civil Engineering Department
Illinois Institute of Technology
Chicago, Illinois
INTRODUCTION
The foam separation of anions from aqueous solution holds promise for the
treatment of industrial wastes, not only enabling the removal of objectionable materials from the effluent but also permitting the recovery of specific anions in a
concentrated, collapsed foam stream. The concentration of anions from extremely
dilute solutions may allow more accurate analyses for objectionable or toxic materials. Phenol(l,2), orthophosphate(3), and dichromate (4,5,6) have been foam
separated with a cationic surfactant, employing batch operation. Dichromate
(6,7) has been foam separated using a continuous flow unit. In these studies, independent variables have included feed anion concentration, feed surfactant concenttation, pH, the presence of interfering anions, gas flow rate, detention time,
and feed position. Upon contacting phenol or phosphate with the cationic surfactant, all species remained dissolved in solution; the mechanism of the foam
separation process involved either the formation of a soluble, surfactant anion
complex which was adsorbed at the air-aqueous solution interfaces of the foam
producing bubbles or the adsorption of the surfactant at the interfaces followed by
the electrostatic attraction between the surfactant and the oppositely-charged
anions. Upon contacting dichromate with the cationic surfactant, a second phase
was formed consisting of colloidal size-particulates; the surface-active particulates
were then adsorbed at the bubble interfaces and floated from solution.
The objective of this study is first, a comparison of the residual ratios obtained from the batch foam separation of phenolate, orthophosphate, and dichromate, including the effects of pH and of the initial surfactant concentration; and
second, the establishment for the first time of the feasibility of multicolumn, continuous ion flotation of dichromate for the removal and recovery of hexavalent
chromium.
BATCH FOAM SEPARATION OF PHENOLATE,
ORTHOPHOSPHATE, and DICHROMATE
Experimental
A schematic diagram of the experimental apparatus used is presented as Figure
1. Details of the apparatus and procedure have been reported previously
(1,2,3,4,5,6). The filtered nitrogen gas was saturated with water, metered with
a calibrated rotameter, and passed through diffusers of approximately 50 micron
porosity. For phenolate and orthophosphate, the nitrogen rate was about 400 ml/
min at 25 C and one atmosphere; for dichromate a nitrogen rate of 4250 ml/min
was required due to decreased foam volumes produced by dichromate and to the
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