PHOENIX Fines Processing Systems

Producers of construction materials are confronted with a changing business environment today relating to materials specifications, production costs, the availabilities of reserves and water, and environmental regulations.

The economic management of wastewater and residual fines is essential to successful and profitable operations. In the past, plants would normally deposit effluent wash plant slurry containing fine sand, silt, and clay into a containment area or slurry pond. Technological improvements in particle separation, water clarification, and fines dewatering offer economic benefits to producers. Slurry ponds can be eliminated, freeing up mineable reserves and eliminating costly environmental liabilities.

Sand specifications that essentially eliminate the use of minus 200 mesh material for many projects can further complicate the slurry pond problem. To remove virtually all minus 200 mesh material from sand production, the amount of plus 200 mesh material in screw classifier overflows is increased. This increase in rejects reporting to slurry pods makes it even more important to have a well conceived plan for effectively dealing with residual fines.

PHOENIX Model HG Separator First Phase

PHOENIX for many years has offered a phased solution to fines slurry processing, consisting of solids separation followed by thickening and dewatering of the slurry. Depending on the particle size distribution in the slurry and the desired objective of the aggregate producer, the solution can consist of one, two, or three phases. The percentage of reject material in the minus 200 mesh x 400 mesh range, defined by lab testing of a slurry sample by PHOENIX, determines if it is economically practical to mechanically separate, dewater, and recover this fraction.

If there is a significant percentage of plus 400 mesh fines in the sand screw overflow and the producer wants to recover this fraction, the first (separation) phase can reclaim and dewater the plus 400 mesh fines and reject the minus 400 mesh material. The Model HG, consisting of hydrocyclones and dewatering screens, performs this operation without using polymers. Without any further processing this dependable technology reduces the amount of material reporting to the slurry pond, while extending the pond’s life. However, this technology alone will not totally eliminate the need for ponding. The minus 400 mesh overflow must still report to a pond, where the fine solids settle out and the surface water recirculates to the wash plant.

To dispose of these reject fines more cost effectively, PHOENIX applies, as a second (thickening) phase, its Model AF AltaFlo™ or its Model HF Hi-Flo™ Thickener. These sedimentation technologies maximize the recovery rate of water, provide cleaner water for recycling, and reduce the slurry flow rate while thickening the slurry from 5–10 percent solids to 40–45 percent. The resultant volume reduction factor is as much as eight to 10 for the slurry going to either the final dewatering stage or to the slurry pond. The thickener overflow, available for recycling, generally contains less than 100 parts per million (ppm) of suspended solids. Sedimentation thickening uses polymers to agglomerate fine particles, increasing the solids settling rate. Thickeners can reduce the size of slurry ponds by immediately returning 75-80 percent of the process water to the wash plant; however, they cannot totally eliminate the need for slurry ponds. The thickened underflow must still be accommodated in some way.

PHOENIX Model WX Belt Filter Presses have been dewatering liquid phase thickener underflows since 1984. This third (dewatering) phase converts these underflows from 40-45 percent solids to a stackable state in the range of 70 percent solids. This dewatered “cake” is conveyable, haulable, solid phase, handleable material. The belt press feed (thickener underflow) is first dosed with flocculant as it passed through an in-line mixer and is distributed evenly across the gravity zone belt. Passing through the gravity drainage section, wedge zone where the two press belts converge, and finally through the compression/shear zone the thickened slurry is gradually dewatered. The filtrate water is pumped back to the PHOENIX Model US or Model HF Thickener, where the water is clarified and then recycled back to the wash plant. The dewatered “cake solids” are then available for disposal or for sale and use in one of many post dewatering applications.

PHOENIX Process Equipment Co. is a leading global supplier of systems for separation, classification, thickening and dewatering dredged sediments, coal tailings, and other minerals slurries and for dewatering sludge from wastewater treatment systems.

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