Sand Separation Techniques

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Sand Separation Techniques

Background

There are different levels of contaminated soils within the river and

estuarine systems of industrialized Europe. Many of the contaminated

materials have medium to large percentages of sand associated with the

finer-grained contaminated materials. Due to limited disposal areas and

the high cost of handling contaminated materials, many countries employ

sand/silt separation techniques. The Netherlands requires that sand be

separated from the fine-grained fraction when handling contaminated

materials. Several methods have been developed, ranging from simple to

complex.

Technology

One of the separation systems is located in Hamburg, Germany, along

the Elbe River. In 1993, the Metha plant (Mechanica Treatment of Harbor

Sediments) began separating the coarse and fine-grained fraction of con-

taminated sediments dredged from the Elbe River (Detzner et al. 1998).

Figure 8 shows the operating principle of the plant. Dredged materials

are temporarily held in a 300,000-m3 holding basin, and then material

passes through a coarse fraction (larger than 80 mm) bar sizer to reduce

clogging downline. Two hydraulic dredges are then used to pump the sedi-

ment through a rotary screen to remove particles greater than 10 mm. The

sediment then passes through hydrocyclones to separate the coarse frac-

tion. Sediment greater than 63 microns is separated from the fine-grained

fraction, and the sand passes through an ascending flow separator to re-

move the remaining fine particles, as well as other debris. The sand is

next processed through a vibration screen to reduce moisture content to be-

tween 10 and 15 percent.

To complete the process with fine-grained sediments, flocculates are

added to decrease settling time; the remaining contaminated material is

processed through a series of presses to reduce the water content to

45-percent solids. The contaminated sediments are then placed in one of

two silt hills or used in the manufacture of bricks (ETH Unwelttechnik

1998; Harms 1995). The plant is designed to handle between 700,000 and

800,000 m3 annually of the 2 to 3 million m3 dredged annually from the

Elbe River.

Chapter 4

Detailed Evaluations