Impact of Sodium Silicate on Paper Machine Drainage and Deposits

Abstract

Over the years antidotal and specific mill observations have been made of sodium silicate carry over from the recycle process impacting drainage and contributing to deposition issues. Sodium silicate has been shown to have benefits beyond being a bleaching aid in the flotation deinking process but the observations of issues at the paper machine has raised concerns. Lots of work and interest has been spend in developing a sodium silicate replacement for pulping chemistry and field testing to date looks good and promising. Benefits obtained from the sodium silicate replacement in pulping chemistry are as follows :
•Similar DIP quality
•Lower anionic trash carry-over from the pulp mill
•Lower process conductivity in both pulp mill and paper machine
•Improved yield by lower reject consistency
•Improved pulp mill performance and paper machine runnability
•Lower overall chemical cost
Recent work looking at replacing sodium silicate in the recycle plant has given opportunities to observe the difference in drainage time, turbidity and deposition behavior. This paper will first discuss the difference in drainage in a polymer only and polymer⁄nano-particle silica retention and drainage program when sodium silicate is not used in the deinking process. Then show how sodium silicate interacts with paper coatings to form deposits potentially harmful to paper machine performance using tackiness measurement in conjunction with colloidal stickies concentration.