PROJECT DESCRIPTION
BACKGROUND
In Europe (including Russia) there are over 30 phosphoric acid plants producing phosphogypsum (PG) as a by-product. The total annual production of PG is more than 21 million tonnes. Kemira Chemicals in Siilinjärvi produces around 1.3 million tonnes of PG every year and only a small amount of this is used. Over 20 million tonnes of PG is stored near the Siilinjärvi plant and this is increasing all the time. Many other branches of industry are also having similar problems with by-products. For example, power plants in the EU are producing 42 tonnes of fly ash (FA) per year, for which they are constantly searching for new ways of recycling and re-using.
OBJECTIVES
The aim of the project was to develop a management system for increasing the utilisation of industrial PG and FA as soil construction materials in an environmentally safe way. The increased utilisation of these by-products contributes to sustainable development by saving significant quantities of natural soil material, by protecting ground waters and natural landscape, and by reducing the amount of industrial wastes. The demonstrative project for the utilisation of industrial PG and FA was carried out on a pilot plant scale using three management tasks. The first task consisted of laboratory tests on the mixtures of PG, FA and divergent binders. Water permeability, compression strength, frost stability and leaching of mineral elements from the mixtures were tested. In addition, the task included estimations of the factors affecting material quality, and the quality assurance system and improvements needed in the processes in order to control and eliminate factors of uncertainty in manufacturing the material. The second task was about the construction of the two demonstration pilot sites: landfill and road construction. In these pilot constructions, different mixing, compression and insulation technologies were tested. The third task concerned the technical and environmental impact assessment and included the monitoring of technical index characteristics, hydrology and mineral element diffusion in the soil. The monitoring data was used for the dynamic model creation in order to calculate the environmental impacts on the specific landfill and road construction projects. Finally a design guide was compiled for the future utilisation of PG and FA in soil construction in a technically and environmentally safe way. A detailed dissemination plan ensured that the project results could be further exploited.
RESULTS
The technical aspects of the project are now finished. The project has provided a means of investigating the applicability of phosphogypsum as a road construction material and as a sealing material (mainly to protect ground water). The construction and renovation of two pilot roads was completed. The first pilot road used phosphogypsum and gravel as structural materials, without compromising technical properties. The second pilot road concentrated on sealing the road (or rather the leaks, liquid emissions) from the groundwater. Both pilot projects were monitored and the results were encouraging: i.e. the phosphogypsum material can be used with conventional road construction materials. The leaching properties still need improvement. A good design manual was also produced, which is now being distributed, mainly through the website. The large-scale use of phosphogypsum in road construction, as a replacement for virgin materials, is still a long way off however. The main obstacles are economic ones. Phosphogypsum is available in only a few places, which makes transportation expensive in comparison to traditional materials, which are more widely available. The overall assessment is that the original objectives were achieved and that the tasks indicated in the application were fulfilled. The management system was developed and tested and the results were very positive. The stabilisation of the old road was very successful for both sites, and strength development and the bearing capacity are clearly better than in the reference sections, or even the laboratory tests in task 1. The structural course sections did not meet the expectations concerning strength development and the bearing capacity and showed no difference to the reference group. The condition of the section has remained excellent however, which indicates that the mix is very resistant to frost damages. The results from the groundwater protection section did not show adequate impermeability with respect to the hydraulic barriers. The technical aspects of the project are now finished. The project has provided a means of investigating the applicability of phosphogypsum as a road construction material and as a sealing material (mainly to protect ground water). The construction and renovation of two pilot roads was completed. The first pilot road used phosphogypsum and gravel as structural materials, without compromising technical properties. The second pilot road concentrated on sealing the road (or rather the leaks, liquid emissions) from the groundwater. Both pilot projects were monitored and the results were encouraging: i.e. the phosphogypsum material can be used with conventional road construction materials. The leaching properties still need improvement. A good design manual was also produced, which is now being distributed, mainly through the website. The large-scale use of phosphogypsum in road construction, as a replacement for virgin materials, is still a long way off however. The main obstacles are economic ones. Phosphogypsum is available in only a few places, which makes transportation expensive in comparison to traditional materials, which are more widely available. The overall assessment is that the original objectives were achieved and that the tasks indicated in the application were fulfilled. The management system was developed and tested and the results were very positive. The stabilisation of the old road was very successful for both sites, and strength development and the bearing capacity are clearly better than in the reference sections, or even the laboratory tests in task 1. The structural course sections did not meet the expectations concerning strength development and the bearing capacity and showed no difference to the reference group. The condition of the section has remained excellent however, which indicates that the mix is very resistant to frost damages. The results from the groundwater protection section did not show adequate impermeability with respect to the hydraulic barriers.
