# Life Cycle Assessment of Mortars Produced Partially Replacing Cement by Treated Mining Residues
## 1 Introduction  
In 2020, the release of greenhouse gases from building operations achieved 10 Gt CO\({}_{2}\), being the highest level ever reported. Together with manufacturing, transportation and construction materials' uses, this represents 38% of global energy-related CO\({}_{2}\) emissions [1]. Climate change and rapid urbanisation with growing population have prompted an emerging interest on construction industries to include more sustainable practices. To accomplish a net-zero carbon building stock in 2050 [2], direct and indirect building CO\({}_{2}\) release needs to be reduced by an average of 55% [3]. Furthermore, the emissions from the production of construction materials, and the construction itself, are mainly driven by cement and steel manufacturing. Their growth in use is the main contributor to buildings embodied carbon emissions. Around 50% of the cement demand comes from the construction sector, being imperative to reduce its use and replace cement by materials with lower embodied carbon [1]. The growing conscientiousness of mining residues impacts have empowered the study of feasible reuse options to reduce waste disposal, concerning a circular economy perspective and the Sustainable Development Goals [4]. Mining activities have reported high amounts of rejected fractions for hundreds of years, as a result of concentrate production. The accumulation of mining residues overtime, in open air impoundments, have led to an intense environmental degradation [5]. The contamination risks for the involved communities are a consequence of the emissions from chemical processes during concentrate production. Nitrogen and cyanide substances may reach aquatic systems, contributing to eutrophication and loss of biodiversity in water streams [6]. Sulfide minerals may contain harmful metals and metalloids, that could promote the formation of acids when in contact with water and oxygen, intensifying acidification phenomena [7]. On the other hand, fines and other particles may be released by the wind, increasing the cross contamination in the region [8]. To tackle climate change issues, the reuse of mining residues in construction products have been studied [9]. Mining resources were applied in geopolymers [10], innovative alkali-based materials for road pavement applications [11], red clay bricks [12], and light-weight construction products [13], with eco-efficient gains in mechanical strength, thermal stability, chemical and fire resistance, and costs [14]. In particular, the use of mining residues in mortars may improve their chemical and structural stability, although some research works reported low replacement cement percentages (e.g., 5%) as effective for materials' requirements [15]. In this sense, the continuous optimization of secondary resources reuse to achieve a higher replacing rate of the virgin material in construction products manufacture, is also important. The electrodialtytic (ED) process is a long-proven technology to remove substances of environmental concern from matrices, as well as to overcome raw materials' shortage and to contribute towards clean energy transition [16]. The ED process is based on the use of a direct low-level current intensity, in pairs of inert electrodes, that promotes the transport of contaminants by electromigration, electroosmosis, and electrophoresis mechanisms [17]. In comparison to metakaolin production and effect [18], the thermal treatment is also regarded as a strategy to take advantage of amorphous silica and/or alumina from fine secondary materials, conferring them pozzolanic properties whilst increasing the durability proprieties of final products [19]. Both ED and thermal treatments were applied to mining residues, and the treated material was used to replace cement in mortars production. The mortars produced with treated mining residues demonstrated positive achievements, and comprised the requirements needed for rendering, plastering, joint repointing, bedding masonry, or scrap uses [20].