Zeta potential analyzer

DLS (Zeta Potential Analyzer, Brookhaven Instruments, Gaia Science Pte. Ltd.) analysis was performed using disposable single sealed cuvettes (size: 50–2000 μL, Eppendorf) containing 200 μL of the leachate solution and BIC Particle Sizing software (Brookhaven Instruments). The effective diameter was detected in five measurement cycles (each cycle running for 1 min) at a scattering angle of 90 °. The light percent distribution and number percent distribution were also detected to verify and compare the particle size distribution.

Both coal
sample and silica were ground to −30 μm using an Agate
pestle for the ζ-potential test. HCl (25.00% v/v) and NaOH (99.99%
grade) were used for pH adjustment. The concentration of KCl used
as the supporting electrolyte was 10^–3 M. Distilled
water was used in the whole process. The procedures were as follows:
0.2 g of sub-bituminous coal or silica was put into a 100 mL beaker,
and the supporting electrolyte close to 100 mL was added. Then, the
pH of the pulp was adjusted to different values after sufficient mixing.
Afterward, the pulp was transferred into a 100 mL volumetric flask
and 0.57 mL of 1% Lilaflot D817M was added into the volumetric flask.
The cap of the volumetric flask was tightened, and the flask was shaken
up and down three times before putting it into an ultrasonic water
bath for 15 min to diversify the pulp well. Last, the volumetric flask
was taken out from the ultrasonic water bath and 1.5 mL of the supernatant
was extracted for the ζ-potential test by a pipette after 15
min standing. The zeta potential analyzer used in this research is
manufactured by Brookhaven Instruments Corporation. Every sample was
tested 10 times, and the average values were taken.