Flocculation of kaolin and kanto loam by methylated soy protein

In this study, methylated soy protein (MeSP) was applied to the solid–liquid separation or flocculation of kaolin and kanto loam (deposits of volcanic ash) suspensions (3.0 g/L). The flocculation performance of MeSP was evaluated in terms of supernatant clarity (jar test method) and floc settling rate (sedimentation balance method), and compared with those of chitosan and polyaluminum chloride (PAC). At pH 7, the optimum dosage of MeSP, chitosan and PAC were almost the same (about 1.5 wt.% of the suspended solids), but there was a remarkable difference in the floc settling rate. At the optimum dosage, the settling rate of the floc formed by MeSP was 6–7 mm/s, while those formed by chitosan and PAC were about 2 mm/s. MeSP showed the highest flocculation performance at pH 3–7 among these flocculants. At pH 8–12, the flocculation performance of MeSP was much higher than that of PAC, but lower than that of chitosan. The flocculation performance of MeSP for kanto loam suspension was strongly affected by the addition of seawater, while the effect of seawater concentration on the flocculation performance of MeSP for kaolin was moderate.

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► Soy protein was esterified for using as bioflocculant (MeSP).
► Flocculation performance was examined with kaolin and volcanic ash suspensions.
► MeSP gave high clarity of water and high sedimentation velocity of floc at pH 3–7.
► Flocculation efficiency of MeSP was much higher than those of chitosan and PAC.