The primary compound—chemical formula Ca(HSO3)2—in the sulfite process, the older and less used of the two primary chemical pulping processes. Calcium bisulfite is produced by combining sulfurous acid with limestone. Cooking wood chips in the combination of sulfurous acid and calcium bisulfite dissolves the lignin in the wood and liberates the cellulose fibers. The sulfite process is not well-suited to pulping highly resinous wood, such as pine trees. Its original calcium-based chemicals are unrecoverable, and pollution laws have resulted in newer substances being utilized, such as sodium, magnesium, and ammonia bases, the active chemical in the sulfite process being the bisulfite ion (HSO3-). These bases are easier to recover. The sulfite process is an acidic pulping process, and exists in contrast to the alkaline soda process. (See also Chemical Pulping.)
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