History of the Site
An alkaline chlorine plant was built in 1940 and closed in 1982, in an area covering almost 40 hectares. After a long and complicated litigation and transfer of property rights, the Environmental Protection Agency of Taiwan requested the landowner/owner to carry out remediation in 2009.
Contamination in figures
Over 400,000 tonnes of soil and sediments were contaminated, with total mercury contamination estimated at up to 40 tonnes.
The entire area can be divided into four contaminated areas, including a pond that requires drainage, where mercury was detected at a maximum concentration of nearly 10,000 mg/kg (soil control standard of 20 mg/kg).
Physical Washing Process
Rocks with a diameter of 20 mm or larger are screened out using the rotary washer and rock screen machines. Sand screen and hydrocyclones machines are then operated to screen out pebbles and sand that are between 20~0.075 mm and silt with diameters between 0.075～0.02 mm. The final procedure is to collect mercury-enhanced silt and clay with a diameter less than 0.02mm and pressure press them into mud cakes using high-efficiency filter press.
Chemical Washing Process
Sand and silt screened out from the physical washing treatment are transported into the chemical washing process. Chemicals are applied to transform mercury species that are adhered to the soil surface into mercury complex, which would dissolve in the water. Belt vacuum filter then separates the washed soil from the waste water that contains mercury complex. Waste water is treated, with most of it recycled and the rest drained into the waste water treatment system on site.
Soil washing of mercury is an innovative method for treating contaminated soil. Apollo operated a pilot test for CPDC to prove the feasibility of our soil washing method. After treating more than 140,000 tons mercury contaminated soil at our on-site treatment plant, our client is satisfied with the performance of soil washing treatment.
Apollo Technology Added Value
A successful site remediation depends not only on the concentration of different contaminants, but also on the soil characteristics.
When thermal treatment is chosen as the primary treatment technology, soil cleaning, which can treat several contaminants, can be used as an additional technology, which is often cost-effective when the two technologies are combined.
The soil cleaning technology, which combines physical and chemical cleaning, was then used as a pre-treatment contamination reduction technology and was installed on site on a plant scale.
Note: the photo for the banner is a courtesy of CPDC