The zeta potential is a key indicator of the stability of colloidal dispersions. The magnitude of the zeta potential indicates the degree of electrostatic repulsion between adjacent, similarly charged particles in the dispersion. For molecules and particles that are small enough, a high zeta potential will confer stability, i.e., the solution or dispersion will resist aggregation. When the potential is small, attractive forces may exceed this repulsion and the dispersion may break and flocculate. As such, colloids with high zeta potential (negative or positive) are electrically stabilized while colloids with low zeta potentials tend to coagulate or flocculate (Wang et al., 2011 and Zheng et al., 2011). Fig. 3 shows the trend of zeta-potential on the suspension of Mg-sericite in brewery wastewater. Zeta-potential increased from − 22.3 ± 2.4 mV in the control to + 2.12 ± 0.4 mV with 100 mg/L of Mg-sericite. In the present study, zeta-potential was positively correlated with flocculant dose. Flocculation using Mg-sericite is the result of particle collision and charge interaction between the charges of Mg-sericite and the cell surface in a liquid medium. When particles cluster together as a result of the flocculation process the settling rate increases. The apparent surface charge of the organic/inorganic matter is represented by its zeta potential, which may affect flocculation efficiency (Chen et al., 2014). Duan et al. (2014) reported similarly results that zeta-potential increased with increasing flocculant doses. Zeta potential values ± 15 mV usually represent the onset of agglomeration. The threshold region for either coagulation or dispersion is about ± 14 mV to ± 30 mV. Generally, zeta-potential values from 0 to ± 5 represent rapid coagulation or flocculation, from ± 10 to ± 30 indicate incipient instability and values more electronegative than ± 30 mV usually represent sufficient mutual repulsion to result in stability (i.e. no agglomeration) (Kulsing et al., 2015). In this study, over 80 mg/L Mg-sericite produced in zeta-potential in the range of 0 to ± 5.