PROJECT DESCRIPTION
BACKGROUND
The precipitated silica production process generates a high conductivity salt stream as by-product that is poured into natural channels after passing through treatment plants. The main salt generated in the process is sodium sulphate (Na2SO4) which must be removed, along with other components such as colloidal silica, by washing, generating high water consumption. For each tonne of precipitated silica produced, 0.75 tonnes of Na2SO4 are obtained as a by-product and this generates a discharge of 40 m3 (30 g/l). European production of precipitated silica in 2018 reached 720 000 tons (2 500 000 tonnes worldwide) with big growth expectations during the coming years.
It is estimated that the industry is spilling about 500 000 tons of sodium sulphate into European natural channels. Spills from the precipitated silica industry (as well as other industrial and domestic spills) contribute to an increase in the natural salinisation of rivers. The excess salinity is a factor that conditions the survival of natural organisms and communities, biodiversity, and the ecological balance of the entire ecosystem. This problem is especially important in the summer when river flows are at a minimum, and the salinity concentration can naturally reach maximum recommended parameters (250 ppm-sulphate ion). These saline discharges also generate problems in water treatment and purification facilities, corroding their equipment and slowing down the digestive processes, generating high economic costs for administrations.
OBJECTIVES
LIFE ZEROSILIBRINE aimed to demonstrate the application of an innovate technology for the treatment of precipitated silica wastes, an environmental challenge that had no current feasible solution. The implementation of a circular economy strategy in precipitated silica sector would help mitigate the environmental impact caused by the discharge of the by-product generated (sodium sulphate). This was to be achieved by recovering 100% of the water for the production process itself (reduction of water collection and reuse of the discharge water as process water) and recovering sodium sulphate as a high-purity product with commercial value.
This project was designed by IQE to scale up small-scale results (2m3/h) to a pre-industrial scale (40m3/h) and validate it before the construction of a full industrial installation (120m3/h) after the LIFE project.
The specific objectives were the following:
- demonstration of the technical feasibility of the reverse osmosis stage by means of the 40m3/h installation recovering 80% volume of the production process effluent of precipitated silica reusing the water recovered in the same production process
- validation of the operating costs of the reverse osmosis process and validation of the economic feasibility of the manufacture of high purity anhydrous sodium sulphate
- validation and optimisation of the evaporation-crystallisation stage with a small prototype (1-2m3/h) from 80% to 100% of the discharge volume until obtaining a commercial anhydrous sodium sulphate
- study the anhydrous sodium sulphate by-product characteristics with primary sodium sulphate manufacturer
- study the potential technology replicability and transfer to other chemical processes and/or industrial sectors.
LIFE ZEROSILIBRINE was expected to contribute to achieving the objectives of the EU Circular Economy Action Plan, Water Framework Directive and the EU Chemicals Strategy for Sustainability.
RESULTS
The beneficiaries have successfully achieved the objective of demonstrating the technical feasibility of a solution for the treatment of IQE’s brines. The solution is based on an ultrafiltration and reverse osmosis stage that enables the reuse of the resulting osmosis water and part of the concentrate in IQE’s production process. The process is completed with an evaporation and crystallisation stage to obtain anhydrous sodium sulphate from the portion of concentrate that cannot be reused internally. This anhydrous sodium sulphate can be then put on the market as an alternative to its mineral equivalent.
The pilot plant has a capacity of 40 m3/h and has been operating for more than a year with good technical results. Up to 87% of the effluent volume from the process of precipitated silica is reused as osmosis water in the same production process. The remaining 13%, consisting of concentrated sodium sulphate brine, is partly reused internally, while the rest is further processed through evaporation and crystallisation to produce anhydrous sodium sulphate. IQE has acquired ECHA's letter of access for sodium sulphate, and can market more than 1 000 tonnes/year of this product.
Following the end of the project, additional investments are being made to improve the performance of the crystallisation stage and reduce operating costs, thereby ensuring the economic viability of the pilot plant. In the coming years, the plant will be scaled up to treat all the brine generated by IQE during silica production, fully eliminating any discharge into the Ebro River.
