Polyaluminum chloride with a dominant
species of Al
30
(PAC-Al
30
) was prepared in laboratory
and used for humic
acid (HA) removal from water. The action properties and mechanisms
of PAC-Al
30
, HA, calcium, and kaolin were tested and discussed.
The results showed that the existence of calcium or kaolin contributed
to the HA removal when the PAC-Al
30
dosage was deficient
and had no obvious effect when the amount of PAC-Al
30
was
sufficient. When the PAC-Al
30
dosage was 0.01 and 0.02
mmol/L, the HA removal rate was increased by 66.59 and 42.20%, respectively,
with a calcium concentration of 2.0 mmol/L, or increased by 53.31
and 40.92%, respectively, with the kaolin particle concentration of
150 mg/L. Calcium could compress the double electrical layers or complex
with HA to neutralize a part of the surface negative charge of HA,
but could not make the water system reach its isoelectric point. The
mechanisms of calcium and kaolin’s promoting coagulation effect
were adsorption neutralization and collision aggregation respectively,
but these actions were much weaker than that of PAC-Al
30
with HA. The adsorption neutralization capacity of PAC-Al
30
was calculated to be nearly 60 times than that of calcium, and the
higher γ value of calcium modified by the Sips equation may
indicate that the adsorption or neutralization sites of calcium on
HA were pickier than PAC-Al
30.