Modification of wollastonite by acid treatment and alkali-induced redeposition for use as papermaking filler

• Process flow for modifying wollastonite powder was established.
• Four kinds of alkali-induced redeposition wollastonite powders were characterized and used.
• The morphology and chemical constituents of the modified powders were investigated.
• Modified wollastonite with Na2SiO3 treatment had the most obvious effect in filled paper.

In order to increase the applicability of wollastonite in the papermaking industry, it was modified by an acid treatment and alkali-induced redeposition. The modification process consisted of two steps: first, sulfuric acid was mixed with wollastonite, resulting in the partial dissolution of the wollastonite particles. Next, the pH of the mixture was adjusted to make it alkaline so that the dissolved material was redeposited on the surfaces of wollastonite particles, which maintained their original acicular morphology. The resulting wollastonite particles were larger, had a higher zeta potential, and were brighter than were those of the original sample. The properties of paper sheets, especially bulk and brightness, in which a Na2SiO3-induced redeposited wollastonite sample was used as the filler were superior to those in which the original wollastonite sample or other alkali-induced redeposited wollastonite samples were used.

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