Dredging is crucial for ports and waterways navigability and water and flood management. Complying with the Circular Economy concept, dredged material can be re-used in several ways. Contaminated sediments, although occurring in minor volumes, can be only re-used after special treatment. Strict environmental limits apply to contaminated sediments and their final uses.
Prior to any reuse, sediment shall fit to basic technical parameters for a given application. Depending on the final reuse way, it shall also comply with complex legislation in sea, inland water, waste and soil protection branches.
Sediment cannot be reused in a sludge form. In all cases, it shall be dewatered to obtain typical soil consistency. If contaminated, dredged sediments shall pass special treatment to eliminate its harmful effects. Stabilisation processes are used here to keep all pollutants under control.
Lime can react selectively with individual parts of dredged material and provide:
- Floculation together with iron or aluminium salts; therefore it is widely used in the first treatment step at sediment dewatering processes
- Drying and solidification thanks to exothermic hydration of quicklime when used
- Further dewatering thanks to reaction with clay minerals in sediments, releasing physically bound water; this changes their nature to sandy or granular
- Reduction in solubility of most contaminants in dredging sludge (mainly heavy metals) thanks to alkali pH of lime and preventing them from leaching to environment
- Sediment stabilisation thanks to pozzolanic reaction between lime and clay minerals to solid and low-permeable matrix, contributing to contaminants leaching blockage
For most of sediments, customized lime-containing binders combine the effects above with increased cementitious reaction of hydraulic admixtures. This synergetic effect results in stable and durable final products wherever required.
Carmeuse offers the STABICALCO® range of products targeting the complex treatment, solidification and stabilisation of dredging sludge and sediments.