Waste paper treatment process

摘要

According to the present invention there is provided a method of treating reject from a plant for de-inking waste paper which reject comprises in an aqueous medium a mixture of suspended solids comprising at least ink particles, inorganic particles and fibers, which method includes the steps of (i) chemically treating an aqueous suspension comprising said reject by adding to the aqueous suspension a source of alkaline earth metal ions and a source of carbonate ions to react with the alkaline earth metal ions to form therein a composite particulate material comprising a substantially white insoluble alkaline earth metal carbonate compound precipitated by the said reaction which compound bonds to and entrains material comprising ink particles, inorganic particles and fibers contained in said reject, whereby the darkness of the reject is reduced by formation of the precipitate of the carbonate compound; and (ii) recovering the composite particulate material and delivering the composite particulate material for re-use as a pigment in a process for making or coating cellulosic sheet material.