Retention of Calcium Carbonate During Recycling: Direct Loading Versus Fiber Loading, 1997 Environmental Conference Proceedings

Recycling mills produce two to four times as much sludge as virgin fiber mills, in excess of 200 kg/ton of paper proc-essed. Recycling mills in the United States alone generates an estimated 4.1 million tons (dry basis) of sludge annually. This study compared the retention of calcium carbonate fill-ers by a pulp filled by fiber loading with the retention of calcium carbonate by conventional recycling process. Pulp obtained by both processes were recycled several times using a recirculating handsheet mold to evaluate relative impact on process water and, ultimately, sludge production. About 50% less calcium carbonate was needed to maintain the ash level of fiber-loaded handsheets than was needed for direct-loaded handsheets. Process water from fiber loading contained about 50% less calcium carbonate than the direct-loading control process water. Results indicate that fiber loading can reduce calcium carbonate loss by up to 50% compared with conven-tional direct loading of calcium carbonate. This study also indicates significant total sludge reduction in a deinking mill compared with current direct loading. This handsheet study should be verified by an industrial-scale evaluation.