WHICH CHEMICAL-AGENT SHOULD BE USED FOR BLEACHING OF A DEINKED PULP, HYDROGEN-PEROXIDE OR SODIUM HYDROSULFITE

Brightness of a deinked pulp from newsprint is not sufficiently high t o be used in anew formulation. The pulp is bleached by three different alternatives to meet the requirement of 60% ISO brightness. The first alternative, named ''A'', consists of the addition of 1% hydrogen per oxide in the pulper at the usual deinking condition. The bleaching sta ge is performed subsequently to the deinking process with 0.25% hydrog en peroxide and 0.30% sodium hydrosulphite, alternatives ''B'' and ''C '', respectively. The study shows that alternatives ''A'' and ''C'' of fer more advantages in terms of optical and mechanical properties. We also conducted an economic comparison among the three alternatives bas ed on the difference in operation and investment costs, the operation including manpower, chemical products and energy requirements. The cos ts used are based on the literature to obtain a mean value. For an ann ual production of 120,000 tons, the operation costs reach 2.4, 2.7, 1. 1 million USS and the investment costs are 0, 4.3, 1.3 million USS for alternatives ''X'', ''B'' and ''C'', respectively. Therefore, alterna tive ''B'' is rejected. The choice narrowed down to alternatives ''A'' and ''C'', depending on the economic criteria of each company For exa mple, alternative ''C'' is preferred if the investment period is great er or equal to 2 years for an internal rate of return of 20%.