Portable Dredges Mine Silica Sand for Glass Industry in Millville, New Jersey, USA
Silica Sand is commonly used in the production of a variety of glass products. Portable hydraulic dredges provide an excellent method to economically mine large silica deposits.
US Silica’s Newport Plant used two Ellicott 900 hp diesel dredges equipped with hydraulic cutterheads to mine silica sand in Millville, New Jersey, 40 miles southeast of Philadelphia.
Geological conditions in the area place restraints on the methods by which materials can be mined. Since the water table lies only six to 20 feet below the surface of the ground, and sands are mined to a depth of 40 feet, any excavation fills with water. For this reason, hydraulic dredging is the only practical method to extract and transport materials.
Originally, equipment limitations restricted production at the Newport Plant. In the 1920s a small wooden dredge equipped with a six-inch suction pipe and a six-inch cast iron pump with a 12-inch diameter impeller was used to pump sand a mere 300 feet to the processing plant. Unfortunately, much material was inaccessible due to the thick layers of clay lying below the surface of the ground.
After World War II, the glass industry expanded at a tremendous pace and the silica processing operation was expanded. Additional suction dredges were added with booster pumps to keep production high. Still the subsurface clay lenses inhibited efficient utilization of the silica deposits.
In the 1960s the entire mining and processing operation was expanded and efficiency improved. The first powerful 14-inch cutter dredge was purchased allowing the company to dig through the clay lenses. Production from the minefield tripled.
Care was taken so that the excavated area does not become an eyesore once mining is completed. All vegetation was stripped from the surface before an area was to be mined. After an area was mined out, the perimeter of the open pit is "brimmed" (sloped to a 30 degree angle) and tree seedlings are planted around the rim. The result is a tranquil fresh water lake.
With the more productive nature of today’s hydraulic dredges, efficiency and production at the plant were greatly improved.
The sand, clay, and stones are pumped several thousand feet through a 14-inch floating pipeline to a screening station where the sand product is separated from the oversize material and clay. The sand is transported through a slurry line with a series of booster pumps four miles to the processing plant where the sizing and purification takes place.
First, the coarser sand is separated from the finer sand and is stockpiled for cement customers. Next, the finer grained sands are either ball-milled or delivered directly to the flotation process in which the metallic impurities are removed. The high quality silica is then dried, re-screened and stored to await shipment to glass producers up and down the East Coast.
Since the 1920s millions of tons of silica sand have been mined, processed, and shipped from the company’s plant. In exchange for the valuable silica sands, the operation has left behind a series of serene lakes bounded by forest, and stocked with fresh water fish.
Reprinted from World Dredging & Marine Construction
