Geotube® Dewatering and Containment of Gypsum Wastes at a Titanium Dioxide Plant

Industrial wastes are typically in slurry form and may contain large amounts of contaminants that requires proper management and disposal in an environmentally acceptable manner. This often requires dewatering, then deposition at a secured landfill. This case study describes the use of geotextile tubes to dewater gypsum waste slurry at a Malaysian titanium pigment plant. The plant produces titanium pigments by digesting ilmenite in sulphuric acid, commonly known as a sulphate process. The process involved discharging red gypsum waste in the form of slurry with a solid concentration of about 16% that was treated using filter presses (Figure.1).

The challenge

The plant faced a problem with capacity and storage. Its filter presses were operating at maximum capacity and all sludge lagoons were full. The high capital expenditure is associated with adding additional filter press capacity and the low rate of return on investment motivated the plant to explore less costly alternatives of dewatering the sludge.

The Solution

The client decided to explore the option of installing Geotube® dewatering units as proposed by specialist engineers from TenCate as part of a more integrated plant processing solution.

A Rapid Dewatering Test (RDT) or Jar Test evaluation of the sludge was first carried out to determine the polymer type and dosing rate needed to flocculate the sludge. The results of these tests confirmed that the correct dosage was applied and Geotube® GT 500D fabrics could contain and dewater the red gypsum slurry. The discharge was visually clear effluent of good quality (Figure 2). The results of the RDT tests was further confirmed by undertaking a Geotube® Dewatering Test (GDT – Figure 3) or Pillow Bag test. Finally, a full scale pilot tube utilizing Geotube® GT500D fabric with a circumference of 8.8m and length of 27.5m (Figure 4) was pumped with appropriately dosed effluent in order to identify future operational implications and confirm actual solid volumes contained within the tube. The trial confirmed a 39% dewatered solids concentration.

More than 100 units of Geotube® dewatering tubes with a circumference of 36.6m and lengths between 57m and 43.8m, stacked four levels high was installed over a year as part of an integrated plant waste capture program. A total of 180,000m3 of dry solids was captured within the tubes. Using Geotube® dewatering tubes saved the client CAPEX and reduced their overall maintenance and operational costs.

Works Implementation

Prior to deployment, the position of the Geotube® units were marked on the geomembrane liner. Each Geotube® dewatering unit weighing about 1.3 tons required lifting and positioning by a mobile crane. The Geotube® dewatering units were then unrolled and unfolded manually by the operators or by a mechanical winch attached on a 4WD vehicle. A 100 mm diameter flexible hose was used to connect the slurry main pipe to the Geotube® dewatering units. The filling ports of each Geotube® dewatering units was connected with flexible hoses and the slurry inflow for each port was regulated by a gate valve installed between the main slurry pipe and the flexible hose.

The Performance

Tencate Geotube® dewatering technology increased the plant’s dewatering capability by approximately 25% and enabled the plant to accommodate the sudden surge in demand for titanium dioxide. The plant could also do a complete maintenance overhaul of their aging mechanical dewatering equipment without affecting production.

The filtrate quality discharged from TenCate Geotube® dewatering units was of significantly higher quality than what could be achieved using the filter presses further reducing processing costs.