Investigation of stabilization and destabilization possibilities of water alumina suspension in polyelectrolyte presence

• Alumina suspension stability in polyacrylic acid — PAA presence was studied.
• Turbidimetry method was applied to monitor stability changes at pH 3, 6 and 9.
• PAA at pH 9 causes considerable improvement of suspension stability.

Adsorbed polymers show stabilization–flocculation properties of colloidal suspension and they are widely used in technological applications (chemical and pharmaceutical industries, food processing, drinking water purification and wastewater treatment). Thus, the influence of polyacrylic acid (PAA) addition on the stability of synthesized alumina suspension as a function of solution pH was studied. The changes of the examined systems stability in time were monitored using the turbidimetry method. It was shown that the alumina suspension without the polymer is the most stable at pH 3 (electrostatic stabilization), whereas at the pH values 6 and 9 the systems are unstable (coagulation). The addition of PAA with the lowest molecular weight (i.e. 2000) at pH 3 causes large deterioration of the system stability (destabilization by charge neutralization), whereas at the pH values 6 and 9 significant improvement of analogous system stability is observed (electrosteric stabilization). PAAs with higher molecular weights (100 000 and 240 000) cause stabilization of the alumina suspension in the whole range of studied pH. At pH 3 it is rather steric stabilization. On the other hand, at the pH values 6 and 9 the steric mechanism of stabilization is combined with the electric one, leading to electrosteric interactions.