Recycling of mineral wool waste as supplementary cementitious material through thermochemical treatment.

Mineral wool is commonly used in construction as thermal insulation material. After the product's lifetime, it is classified as hazardous waste if no trademark of the European Certification Board for Mineral Wool Products (EUCEB) or the German Institute for Quality Assurance and Labelling (RAL) exists. Mineral Wool Waste (MWW) is typically landfilled in Europe, which is challenging due to its low bulk density and dimensional stability. This circumstance highlights the need for alternative recycling methods that increase the recycling rate of construction and demolition (C&D) waste. This article outlines the recycling opportunities of MWW and focuses on the use of thermochemical treatment of different mixtures of input materials to produce a supplementary cementitious material (SCM). The material characterisation results and investigations on the binder suitability demonstrate that the slag fractions after the thermochemical treatment are well-qualified to be used as reactive binder components. Additionally, a material flow analysis was conducted to estimate the substitution potential of MWW as SCM in the Austrian cement industry.

Valorisation of metallurgical residues via carbothermal reduction: A circular economy approach in the cement and iron and steel industry.

The decarbonisation of the steel and cement industry is of utmost importance in tackling climate change. Hence, steel production in modern integrated steel mills will be shifted towards electric arc furnaces in the future, in turn causing dwindling supplies of blast furnace slag, which is used as a supplementary cementitious material inter alia to reduce the CO2 emissions of cement production. Achieving a sustainable circular steel and building material economy requires the valorisation of currently landfilled steel slags and investigating utilisation options for electric arc furnace slag, which is increasingly being generated. For this purpose, different metallurgical residues and by-products were treated by carbothermal reduction in an inductively heated graphite crucible and then rapidly cooled by wet granulation, yielding a slag fraction similar to granulated blast furnace slag and a metal fraction valuable as a secondary raw material. A spreadsheet-based model was developed to calculate residue combinations to accomplish target compositions of the slag and metal fractions to fulfil previously identified requirements of the targeted cementitious and ferrous products. The results demonstrate the high accuracy of the model in predicting the properties (e.g. main oxide composition) of the generated slag and metal fraction, which fulfil the needed requirements for their use as (i) a supplementary cementitious material and (ii) a secondary raw material in steel production.