What is Washing?

Washing is the separation of silts and clays from the sand and stone

Why do silts and sands need to be separate from sand and stone before use in concrete, etc.?

Clay and high levels of silt in sand and stone used in concrete, etc. causes weakness/faults in the finished concrete product

What is clay, silt and sand?

Clay can be defined as particles smaller than 2 microns. (1, microns = 1mm)

Silt is generally accepted as particles 2-75micron. (In some EU countries 2-63 micron.)

Sand is normally taken as particles 75micron - 4mm

What is the washing process? 

The clay, silt and sand fraction is separated from the larger stone fraction over vibrating screen fitted with a boiling box and fresh water spray bars fitted with jets/nozzles.

The cleaned stone product passes over the screen whilst the clay, silt and sand fractions pass through the screen and flow with the water into the Hydrasander.

In the Hydrasander the sand is collected and dewatered by the bucket wheel whilst the silt and clay portion leave with the waste water

How does the Hydrasander separate the clay and silt from the sand?

The sand particles, i.e. particles 75 micron to 4mm, gravitate to the base of the Hydrasander tank where they are removed by the spiral and bucket wheel. The clay and silt particles are much finer so remain in suspension until the water has passed through the Hydrasander.

	What Happens the clay and silt after it leaves the Hydrasander with the waste water?    The waste water from the Hydrasander normally travels to large settling ponds where the clay and silt settles out. The water is then pumped back to the washing plant for reuse. Alternatively, the waste water can be cleaned through a mechanical system such as a Siltmaster.

Is the stone product always clean enough after being washed over the screen? 

In some cases where clay and silt lumps are present it is necessary to pass the stone through a Logwasher to remove these from the stone. The Logwasher is normally located after the washing screen and removes the clay and silt lumps with blades mounted on two inclined shafts ("Logs") as the material passes through the unit. The clay and silt lumps that have been broken up inside the Logwasher leave with the waste water in a similar fashion to the Hydrasander