California producer eliminates the need for settling ponds and captures water for reuse.

Any time an aggregates producer can provide sound environmental practices while improving its own profitability, it is on the winning side of the production equation. Sustainability in the aggregates industry is a business approach that has gained considerable attention in the past several years. The BoDean Co., Inc., of Santa Rosa, Calif., however, has applied a sustainable approach to its business practices almost from day one.

Dean and Belinda (Bo) Soiland opened BoDean Co. in 1989 with the purchase of the Mark West Quarry in the northern Napa Valley. The quarry has been in operation since 1910, and the Soilands put plans in place not only to reclaim mined-out land, but also to begin using a benching method as they continued to mine. Over the past 20 years, this system of benches has improved safety and operational costs, remediated stormwater runoff, and helped to better manage the mine plan in general. BoDean Co. has since applied the same practice to its newer Blue Rock Quarry in Forestville, Calif.

Filter cakes are being sold to Napa Valley wineries for use as pond liners.

Both the Mark West Quarry and the Blue Rock Quarry supply aggregate material for customers in the surrounding area, as well as to BoDean Co.’s vertical asphalt operation in Santa Rosa. In 2006, in order to combat the cost of purchasing sand for its asphalt plant, BoDean installed a washing plant at the Mark West Quarry and began to produce its own sand. The wash plant includes a blademill, washing screen, cyclone, and dewatering screen. At the same time, BoDean opted to install a Phoenix HiFlo circular thickening plant and an overhead beam Diemme GHT 1500 P13 recessed-plate-frame filter press at the end of the washing stage to capture and reclaim as much water as possible.

Fresh water circulates to its own tank for use in the plant while the underflow thickens to about 50-percent solids and is sent to the filter press.

According to Robb Folmar, site manager for the Mark West Quarry, “We don’t have space for settling ponds, and water is hard to come by here with just a pond above the plant and a creek below.” In addition, the footprint shared by the processing plant and loadout area within the quarry is very tight. Because of this, he says, the wash plant operates in a closed circuit with fresh water coming off the thickener over a weir through gravity overflow to a fresh water tank, pumping back to the wash circuit. The underflow thickens from about 4-percent solids by weight to about 50-percent solids. This mud slurry feeds the filter press, which removes the remainder of the water and produces hard cakes of filtered fines that are up to 90-percent dry.

A make-down system mixes dry batch polymer flocculants with water and injects the polymer into the slurry upstream of the thickener.

The use of belt presses to claim moisture from fines is not unusual in North American aggregate operations. The application of plate presses for aggregates dewatering, however, is new in the United States. BoDean Co.’s plate press, manufactured by Diemme S.p.A. of Italy (now represented in the United States by Louisville, Ky.-based Phoenix Process Equipment Co.), operates by compacting mud slurry between 140 vertical plates that are each about 5-foot square, until the end product is a dry cake that drops beneath the press for loadout.

“Dean had seen Diemme presses used in mining in Europe, and he thought the method would work well for us,” says Folmar. “He is really good at looking forward to the bigger picture and applying his ideas to the company.”

Pumps fill the spaces between the plates with the thickened slurry mixture. The plates work like a mold as they tighten to 225 pounds per square inch of pressure to filter water and create 300-pound filter cakes.

The washing and dewatering plants were installed and running by mid 2006. Folmar explains that fines-laden water slurry captured from the wash plant is pumped to the circular thickener. A dry polymer make-down system mixes dry batch polymer flocculants with water and injects the polymer into the slurry upstream of the thickener. The flocculants attach and help the fines to settle more quickly to the bottom of the tank. The clarified water at the top of the thickener tank flows over weirs and uses gravity to run into the fresh-water tank, where it is pumped back to the wash plant for reuse. BoDean Co. owner Dean Soiland explains that, while a system of totes can be installed to premix the flocculants, he prefers having his crew mix each 250-gallon batch individually for better control. This is because plate presses typically require significantly reduced polymer usage.

From the bottom of the thickener, the slurry of 50-percent solids pumps to holding tanks adjacent to the filter press. A nuclear densometer calculates mud density as it enters the press.

“The press works over pressure and time,” says Ian Scroggins, wash plant operator for the thickening/filter press system at the Mark West Quarry. Scroggins explains that each press plate is covered by its own filtering cloth. The plates hang vertically in a row. At the beginning of a cycle, pumps fill the spaces between the plates (called chambers) with the thickened slurry mixture. The plates work like a mold as they slowly tighten to 225 pounds per square inch, compacting the fines between them and filtering the water first through the outer layer of mud, through the cloths, and finally through holes in the plates to be captured beneath, where it is sent back to the fresh-water system.