טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentHalaui Rafi
SubjectSeparation of Heavy Metal Precipitates from a Dilute
Aqueous Suspension
DepartmentDepartment of Chemical Engineering
Supervisor Professor Emeritus Abraham Marmur


Abstract

In this work a new separation process of heavy metal precipitates was developed for dilute aqueous suspensions. This is done by transfering suspended particles from the aqueous phase to a hydrophobic phase (oil). The oil is dispersed in the aqueous phase by mixing and the particles attach to the dispersed drops due to their  wetting properties. When the mixing is stopped the two liquid phases separate. The oil phase is removed along with the particles attached to it and the aqueous phase becomes sufficiently clean.

This work deals with the separation of copper sulfide precipitates. It was found that this separation method is feasible and successful even without the use of surfactants.

The effect of suspending solution composition on the process was studied by adding electrolyte solutions with different counter-ion valencies. It was found that increasing the ionic strength reduced the zeta-potential of both precipitate particles and oil droplets. Thus the electrostatic repulsion between the precipitate particles and the oil droplets was weakened and the attachment of precipitate particles to the oil droplets was enabled. Increasing the valency of the added counter-ion considerably improved the separation efficiency at a lower ionic strength.

It was important to determine the optimal stirring velocity and oil volume fraction to achieve maximal available interfacial area for particles to attach to. The separation process was found to be successful at a small oil volume fraction of 0.1 and a relatively high stirring velocity.

Theoretical calculation shows that the detachment energy of a particle from the oil-water interface reaches high values compared to Brownian energy.

It was also found that the efficiency of separation increased as the precipitate particle effective diameter increased.