Washing and Screening

Regardless of the way in whieh pulps are prepared, all need to be freed of knots, washed and sereened before bleaehing or papermaking. Pulp sereening and washing are eritieal to mill operation. Some of the proeedures for both meehanieal and chemical pulps are briefly described. 

Hydrocyclones have long been used to separate sand, bark and other contaminants from the pulp slurry. 

Screening involves passing stock thorough a perforated screen plate to remove oversized material from the good quality fibres or fines. Screen plates are rigid metal plates in which slots have been cut or punched. There are essentially two characteristics that affect stock behaviour during screening, first the fibres and fines 

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After the chemical treatment, the pulped wood is removed, washed, and screened. Unbleached, brown-colored paper is made directly for this material. Most whitened or bleached paper is made by the treatment of the pulp with chlorine, chlorine dioxide, hypochlorite, and/or alkaline extraction. In general, sulfate-pulped paper is darker and requires more bleaching and alkaline extraction to give a white pulp. 

Compeau et al. (1990) reported a full-scale slurry-phase PCP remediation. The system consisted of soil washing and screening and resulted in clean soil and wash solution. The wash solution was a slurry containing PCP and < 60-mesh-size soil particles at approximately 20% solids concentration. Slurry was treated subsequently in on-site slurry-phase bioreactors. A 50 m3 slurry reactor was operated in batch mode and inoculated by an uncharacterized PCP-mineralizing culture (107 cells/ml of slurry). After 14 days, 370mg PCP/kg slurry had been degraded to below 0.5 mg/kg. For effective biogradation to occur, inoculation was required. 

Small diesel draglines and power shovels were used to mine soft phosphate deposits at the surface in the Tennessee phosphate district of the United States. In this area, mining sites could be as small as 5 acres and located at considerable distances (up to about 150 km) from processing plants. Small, over-the-road dump trucks were used for transport. Mobility of equipment was important in this case. The phosphate ore is a residual deposit remaining from the dissolution of limestones. The subsurface in these areas is composed of irregular limestone pinnacles and solution features small buckets on the draglines (=1 m ) and power shovels were essential in this situation to maximize recovery. Tennessee ores were washed and screened and mainly used in the production of elemental phosphorus in electric arc furnaces,... 

Pulping (mechanical, chemical, semi-chemical, and deinking) Pulp Washing and Screening Stock Preparation Papermaking... 

The plants are hand-cut, mowed, or pulled in developing coimtries, while mechanized harvesting methods are imder investigation in the United States. Ribboning machines are sometimes used to separate the fiber-containing bark before retting for recovery of the kenaf strands. For pulping, the kenaf is shredded or hammermilled to 57-cm pieces, washed, and screened. 

Chem. Descrip. Poiydimethyisiioxane + filler aq. emulsion Uses Antifoam and drainage aid for pulp washing and screening, bleaching, sewage treatment defoamer in food-contact paper/paperboard component of paper/ paperboard in contact with aq./fatty/dry foods Features Highly effective... 

Uses Liq. defoamer for sulfate or sulfite pulp systems, brown stock washing and screening... 

Uses Water-extended economical defoamers for washing and screening CNC Defoamer 1066 [CNCInfl]... 

Most of the world s commercial forsterite comes from Norway, where it is mined in an open-pit quarry its reserves are estimated to run in the billion of tons (45). Forsterite is associated with little gangue material and is quite friable, so it is easily dressed for commercial use by the simple process of crushing, washing, and screening into a number of ready-to-use sizing grades. Forsterite does not have to be precalcined to be used. 

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