Innovative research approaches to gypsum recycling

1 Introduction

During the formation of the new government in the Federal Republic of Germany at the end of 2021, it was agreed to further accelerate the phase-out of fossil fuels. If the phase-out can be realized “ideally” by 2030 [1], the situation regarding the availability of the by-products of coal-fired power generation will get tighter. This also applies to the loss of gypsum from the flue gas desulphurization plants – this is abbreviated to FGD gypsum. With the drop in FGD gypsum, a raw materials gap is opening up, as a consequence of which alternative solutions must be found to cover current and future demand. The recycling of gypsum waste and the use of recycled gypsum (RC gypsum) in industry is one option to offset the loss of the FGD gypsum. In 2020, around 45 000 t RC gypsum was produced from gypsum waste in Germany [3], which corresponds to less than 1 % of the FGD gypsum used in the gypsum-processing industry. So, probably, even a substantial increase in the quantities of recycled gypsum would not satisfactorily close the FGD gypsum gap, which necessitates a search for further solution approaches. Besides new gypsum raw material sources, the development and use of alternative dry building materials can help ease the situation.

The shortage of raw materials is the starting point for the research projects conducted within the framework of the WIR! alliance “Gypsum recycling as an opportunity for the Southern Harz Region” and the research alliance “Resource management and sustainable construction”. They address problems along the gypsum material cycle. The search is for innovative solutions, e.g. to increase the return and collection rate for gypsum waste, the use of alternative resources and reduce the consumption of gypsum.

2 WIR! alliance on gypsum recycling as an opportunity for the Southern Harz region

Following the successful conclusion of the concept phase and a positive assessment, the alliance started on the realization phase in the first six months of 2019. In the scope of the alliance, concrete (cooperative) projects are initiated and conducted in the innovative field of gypsum recycling and related innovative fields of gypsum waste return, processing and recycling. A research advisory board with members representing industry and science ensures independent evaluation of research ideas, research proposals and findings.

The WIR! alliance “Gypsum recycling as an opportunity for the Southern Harz region” is funded in the scope of the funding programme “WIR! – Change through innovation in the region” by Germany’s Federal Ministry of Education and Research (BMBF).

2.1 Alliance partners and region

The WIR! alliance comprises four initial alliance partners. Besides Nordhausen University of Applied Sciences as the alliance coordinator, CASEA GmbH, a company headquartered in Ellrich, and the Bauhaus University of Weimar form part of the alliance. Another partner in the alliance is the Verein für Regionalentwicklung e.V. (Society for Regional Development) in Bleicherode. Fig. 1 shows the alliance region. It covers in the wider sense the areas of the Southern Harz with the natural gypsum deposits that stretch from the west (Osterode) to the east (Sangerhausen) over a length of around 60 km and a width of around 7 km. Besides the initial alliance partners, numerous other regional and national players from industry and science as well as various stakeholders are taking part in the (cooperative) projects.

2.2 Projects

As part of the alliance, nine research projects have already been initiated. Moreover, in 2022, the realization of two further projects currently at the proposal stage is to commence. The first realization phase therefore comprises eleven projects. Furthermore, additional funding has been made available by the BMBF for the scientific initial alliance partners for specific upgrading of the research infrastructure. Fig. 2 provides an overview of the projects and the project partners involved.

Recirculation of material streams containing sulphates (RueGips)

By way of example, in the following, one of the projects is presented. The RueGips project [4] is generally aimed at increasing the recycling rate of gypsum waste, and accordingly to increase the availability of recycled gypsum. Here the focus is on gypsum waste that so far has not or only hardly been sent for material recycling and has therefore been taken out of the material cycle. Part of the project also concerns making provision for the recycling of largest mass of the gypsum waste material stream, namely construction gypsums and optimizing their supply and recirculation.

The project started in spring 2021 is working on the framework conditions for a planned field test. For this purpose, in consecutive steps, the system limits and the survey region were defined and relevant players identified and catalogued in a company database. To capture the starting situation, a committee is working on criteria for the survey and appropriate data collection methods. Building on this collection of criteria, specific questions were designed, collated and categorized in an online questionnaire. This was transmitted to around 200 players in relevant fields of activity in the defined survey region, the Southern Harz region, over summer. Over a period of around eight weeks, those surveyed were able to provide details on gypsum waste in their companies. The response rate was 13 %. The conducted survey (primary data analysis) and comprehensive research (secondary data analysis) form the basis for describing the material streams of gypsum (material stream analysis) in the Southern Harz region as well as in the whole of Germany.

With reference to this material flow analysis, relevant waste streams were identified. Various gypsum waste samples are currently being tested to assess their recyclability. This working step enables the final definition of the waste stream to be investigated as part of a field test, which in turn forms the basis for a collection and logistics concept to be ultimately developed in a follow-up project.

2.3 Outlook for the WIR! alliance

Within the framework of the WIR! Alliance “Gypsum recycling as an opportunity for the Southern Harz region“, important research issues are addressed within the innovative field of gypsum recycling. Besides the ongoing research projects, in 2022 proposals for two more projects will be submitted and these projects initiated in the Alliance’s first implementation phase. The project “Mobilization of gypsum waste based on the example of dental technology and gypsum-containing small quantities of construction waste from private households“ looks at the mobilization of small quantities of gypsum waste, Furthermore, the acceptance of recycled gypsum raw materials is to be improved with the envisaged joint project “Acceptance and sustainability concept for gypsum recycling – creating and fostering acceptance”.

3 Thuringian Research Alliance “Resource management and sustainable construction”

The declining availability of FGD gypsum increases the pressure on the extraction of natural gypsum and aggravates the already existing conflict between nature conservation (preservation of the gypsum karst landscape) and natural gypsum extraction. The research alliance “Resource management and sustainable construction”, which brings together scientific expertise on this issue in Thuringia, is developing potential solutions to close the gypsum gap. This includes the development of new recycling processes for waste materials containing gypsum, research into alternative constructions materials and circular construction methods and the design of post-mining landscapes sympathetic to nature and landscape considerations.

3.1 Alliance partners

The research alliance is composed of four Thuringian research institutions. Besides Nordhausen University (HSN) with the Thuringian Innovation Centre for Recyclables (ThIWert), the Material Research and Testing Institute at Bauhaus University of Weimar (MFPA), the Bauhaus-University of Weimar with the F.A. Finger Institute of Building Materials Science (FIB) and the Institut für Angewandte Bauforschung Weimar GmbH (IAB) are members of the alliance.

3.2 Projects

In the scope of the alliance, since mid-2021 four alliance projects proposed by the Thuringian partners on the subject of gypsum have been funded by the Thuringian Ministry for Economic Affairs, Science and Digital Society with € 3 mill. in total. Fig. 3 provides an overview of the current alliance projects with their coordinators.

Each of the research projects listed in Fig. 3 is funded with € 750 000 €, each alliance partner taking on central coordination in one research project. Nordhausen University is the lead partner working on the project “Development of gypsum construction products that can be non-destructively dismantled and reused for construction of variable, modular usage units” [5]. To boost the Nordhausen site and develop the research infrastructure in these fields, the Free State of Thuringia is supporting the set-up of a research campus with total funding of € 3 mill.

4 Thuringian Innovation Centre for Recyclables (ThIWert)

Affiliated to Nordhausen University with its strong focus on research, the Thüringer Innovationszentrum für Wertstoffe (ThIWert – Thuringian Innovation Centre for Recyclables) was established in 2018 in cooperation with IAB Weimar and Bauhaus University; it is funded by the Free State of Thuringia and co-financed with funds from EFRE (EU).

ThIWert prioritizes application-oriented, interdisciplinary-networked research and technology transfer in resource efficiency. In cooperation with Thuringian Industry, business and science, ThIWert’s goal is to elaborate innovative solutions for current waste management problems and develop new recycling and waste management concepts to create added value for the environment, the people and the companies in the region and beyond.

With the focus on the recycling economy, at the ThIWert test centre, modern machines are available to conduct research into recycling on pilot plant scale. One application focus for saving primary resources by recycling/urban mining is the topic of construction materials recycling, gypsum recycling and alternative building materials.

5 Summary and outlook

The phase-out of coal and the declining availability of FGD gypsum are leading to a rapidly widening gypsum gap in the next years. Nordhausen University of Applied Sciences, together with its research partners, is taking on this challenge and has substantially stepped up its research activities with the financial support of the German government and the Free State of Thuringia over recent years. Building on existing research findings, the following solution approaches are pursued.

Increased recycling of gypsum products and gypsum waste

Development of alternative gypsum sources

Substitution of gypsum products with other materials

New solutions are to be demonstrated – from the reduction of the gypsum content in gypsum construction materials to the development of alternative gypsum-free dry construction materials. Another solution approach is the development of gypsum construction products that can be non-destructively removed and directly reused. For this purpose, the research activities at Nordhausen University within the Thüringer Innovationszentrums für Wertstoffe (ThIWert) are concentrated in an alliance with numerous renowned research partners, e.g. in the WIR! Alliance “Gypsum recycling as an opportunity for the Southern Harz region” or in the Thuringian Research Alliance “Resources Management and Sustainable Construction”.