Method for improving brightness and cleanliness of secondary fibers for paper and paperboard manufacture

A method for adding filler to secondary fibers pulp for manufacture of paper or paperboard products, comprising the steps of:

• introducing secondary fiber pulp slurry into a gas-liquid contactor apparatus at a location upstream of a contact zone thereof, and also introducing an alkaline salt slurry at a location downstream of the introduction point of the secondary fiber pulp and approximate to the contact zone;
• combining the two slurries in the contact zone and immediately contacting said combined slurries with a suitable reaction gas in said contact zone, and mixing so as to precipitate filler complexes onto the secondary pulp fibers;
• and
• using the secondary pulp fiber with filler precipitated thereon for the manufacture of paper or paperboard products.