EFFECTS OF OPERATING VARIABLES ON ULTRAFILTRATION OF FLEXOGRAPHIC PIGMENTS FROM WASH DEINKING FILTRATE

The presence of flexographic printed newspapers in the furnish to a re cycling-deinking plant results in lowered brightness of the secondary fibre product. This is due to the surface chemistry of flexographic pi gment particles, which are hydrophilic and therefore not removed by co nventional flotation deinking. Although washing effectively removes fl exographic pigment particles from fibre suspensions, the resulting fil trate will contain substantial quantities of pigment necessitating cla rification prior to recycling this water to the process or discharging it to the environment. Ultrafiltration has been demonstrated to be a viable technique for the removal of flexographic pigments from aqueous dispersions. This paper describes the results of a statistically desi gned experimental sequence tailored to optimize the ultrafiltration pr ocess for clarifying flexographic pigment dispersions. The operational parameters investigated include temperature, pigment concentration an d surfactant concentration. Response variables used to assess the effi ciency of the ultrafiltration process are permeation rate and stabilit y of operation.