Eco-Friendly Pavements Manufactured from Mixed Recycled Aggregates Obtained from Construction and Demolition Waste: An Industrial-Scale Validation

This study aimed to validate that laboratory-scale results could be commercially replicated when manufacturing marketable precast concrete. Construction and demolition waste (CDW) was separated into two (fine and coarse) recycled aggregates (RAs). Precast paver and kerb units were fabricated by partial or total substitution of natural aggregates (NAs) by RAs. The study involved the comprehensive characterisation of raw materials, including particle size distribution, mineral composition, and elemental composition. Paver blocks and kerbs manufactured with up to 50% RAs showed mechanical resistance (T = 3.7 ± 0.2 and B = 5.3 ± 0.6 MPa, respectively), water absorption between 5.3–5.7%, and abrasion resistance (approximately 20.2 mm), which met the standard requirements (UNE-EN 1340:2004 and UNE-EN 1338:2004). Furthermore, industrial-scale precast pavement units demonstrated strength and durability suitable for heavy traffic areas. A reduction of 13% in cement content could maintain the requirements with a partial RA substitution of 25%, offering economic and environmental benefits. Therefore, it is feasible at an industrial level to replace NAs with RAs, promoting durability and technological properties with a positive environmental impact and considerably reducing CO2 emissions by up to 65%. Overall, pavers with RAs manufactured at the laboratory scale met mechanical standards, and the kerb stones showed improvements in abrasion resistance. On an industrial scale, kerb stones and precast blocks with specific substitutions can meet strength, water absorption, and abrasion requirements, allowing a reduction in cement content.RENSMA Centro para el Desarrollo Tecnológico Industrial (España) Universidad de Huelva (España) Ministerio de Asuntos Económicos y Transformación Digital, Gobierno de España21 página

Fractionation and fluxes of metals and radionuclides during the recycling process of phosphogypsum wastes applied to mineral CO2 sequestration

The industry of phosphoric acid produces a calcium-rich by-product known as phosphogypsum, which is usually stored in large stacks of millions of tons. Up to now, no commercial application has been widely implemented for its reuse because of the significant presence of potentially toxic contaminants. This work confirmed that up to 96% of the calcium of phosphogypsum could be recycled for CO2 mineral sequestration by a simple two-step process: alkaline dissolution and aqueous carbonation, under ambient pressure and temperature. This CO2 sequestration process based on recycling phosphogypsum wastes would help to mitigate greenhouse gasses emissions. Yet this work goes beyond the validation of the sequestration procedure; it tracks the contaminants, such as trace metals or radionuclides, during the recycling process in the phosphogypsum. Thus, most of the contaminants were transferred from raw phosphogypsum to portlandite, obtained by dissolution of the phosphogypsum in soda, and from portlandite to calcite during aqueous carbonation. These findings provide valuable information for managing phosphogypsum wastes and designing potential technological applications of the by-products of this environmentally-friendly proposal.Junta de Andalucía P10-RNM-6300, P12- RNM-226

Valorisation of ilmenite mud waste in the manufacture of commercial ceramic

This paper reports the results of a study focused on the production of ceramic tiles from ilmenite mud (MUD), a waste generated by the industry devoted to the TiO2 pigment production. Ceramic tiles were produced from mixtures of a commercial red stoneware mixture (RSM) with different concentrations of mud (3, 5, 7, 10, 30 and 50 wt.%). The samples were sintered to simulate a fast-firing process. The sintering behaviour of the fired samples was evaluated according to ISO methodologies by linear shrinkage, water absorption and porosity measurements. Both green powder and fired samples were characterised by means of X-ray diffraction (XRD), differential scanning calorimetry (DSC/TG), field emission scanning electron microscopy (FESEM) and bending strength measurements. Moreover, since this activity is a NORM (Naturally Occurring Radioactive Material) industry, the radionuclides activity concentrations were measured by both gamma and alpha spectrometry techniques. Finally, the TCLP leaching test (Toxicity Characteristic Leaching Procedure, USEPA) was performed to assess the risks of the use of undissolved mud tiles from an environmental perspective. The results obtained demonstrated that ilmenite mud can be successfully valorisated in the manufacture of red stoneware ceramic bodies, with even better technological properties than commercial ones. The addition of mud as additive (from 3% to 10%) had a beneficial effect to the sintering processes, improving the bending strength (up to 15%) and reducing both apparent porosity and water absorption (up to 50%).This research has been partially supported by the Government of Andalusiás Project “Characterization and modelling of the phosphogypsum stacks from Huelva for their environmental management and control” (Ref.: RNM-6300) and by National Institution of Higher Education, Science, Technology and Innovation of the Republic of Ecuador – (SENESCYT for its acronym in Spanish), Prometeo Project. Dr. M.I. Martín expresses her gratitude for the contract JAE-Doc_08-00032 to the Spanish National Research Council (CSIC), co-financed by the European Social Fund Operational Programme 2007–2013 Adaptability and Employment Multiregional.Peer reviewe

Construction and demolition waste as recycled aggregate for environmentally friendly concrete paving

Recycled aggregates (RA) from construction and demolition waste (CDW) instead of natural aggregates (NA) were analysed in the manufacture of new eco-friendly concrete. Fine (FRA) and coarse (CRA) recycled aggregates were used in different percentages as substitutes of natural sand and gravel, respectively. The results revealed that the use of RA in percentages of up to 50 wt.% is feasible. Additionally, RA were used to produce paving blocks in accordance with industrial requirements. Thus, values of water absorption lesser than 6.0% and tensile strength upper than 3.6 MPa were obtained, which are similar to those of a reference sample and within the limit values established by the regulations. These results were achieved by reducing the incorporation of cement, thereby saving production costs and minimizing environmental impact

Erato polymnioides – A novel Hg hyperaccumulator plant in ecuadorian rainforest acid soils with potential of microbe-associated phytoremediation

Mercury (Hg) accumulation capacity was assessed in three plant species (Axonopus compressus, Erato polymnioides, and Miconia zamorensis) that grow on soils polluted by artisanal small-scale gold mines in the Ecuadorian rainforest. Individuals of three species were collected at two sampling zones: i) an intensive zone (IZ, 4.8 mg Hg kg−1 of soil) where gold extraction continues to occur, and ii) a natural zone (NZ, 0.19 mg Hg kg−1 of soil). In addition, the percentage of arbuscular mycorrhizal fungi (AMF) colonization was determined in plant roots and seven fungal morphotypes isolated from rhizospheric soil. Results suggest a facilitation role of native and pollution adapted AMF on Hg phytoaccumulation. E.g., E. polymnioides increased Hg accumulation when growing with greater AMF colonization. We concluded that E. polymnioides is a good candidate for the design of microbe-assisted strategies for Hg remediation at gold mining areas. The consortia between E. polymnioides and the AMF isolated in this study could be instrumental to get a deeper understanding of the AMF role in Hg phytoaccumulatio

Treated phosphogypsum as an alternative set regulator and mineral addition in cement production

Various treatments of phosphogypsum samples extracted in Huelva, Spain, curing conditions and incorporation ratios were studied to evaluate the viability of being used as set regulator or as supplementary cementitious material to improve the mechanical behaviour of cement mortars. The physical-chemical properties, mechanical behaviour and environmental impact of these phosphogypsum-based cement mortars were determined. It was concluded that the phosphogypsum treatments and curing conditions influence the mineralogical transformations of mortars and therefore also the mechanical behaviour of the mortars tested. Furthermore, the heavy metal impurities in the phosphogypsum were immobilized in the cement matrix, leading to a clear improvement of the technical properties of cement mortars made with this waste compared to the traditional use of natural gypsum

A Review of the Commercial Uses of Sulphate Minerals from the Titanium Dioxide Pigment Industry: The Case of Huelva (Spain)

This study was focused on the historical evolution of the waste management policy carried out by the Spanish industry devoted to titanium dioxide pigments manufacturing for minimising its environmental impact. This challenge was achieved by modifying the original chemical process and converting the originally dissolved sulphate and sulphuric acid present in the final streams of the factory into sulphate minerals (melanterite FeSO4 7H2O, szomolnokite FeSO4 H2O, and gypsum CaSO4 2H2O). These by-products were physicochemically, mineralogically and radiologically characterised in order to gain basic information for its subsequent commercial use. Some of the uses summarised in this study for both ferrous sulphates are as a supplier of iron to prevent chlorosis, animal food, manufacture of cement (to reduce Cr VI), primary flocculants for ferrous sulphates, magnetite nanoparticle and nano-Fe2O3 formation, production of magnetite concentrate, remediation of polluted soils with metals, and treatment of wastewaters. Red gypsum was analysed as a substitute for natural gypsum in the manufacture of cement, construction materials, inhibitor in soil erosion, and the immobilisation of heavy metals in agricultural soils and carbonation processes.This research was partially supported by the Spanish Government Department of Science and Technology (MINECO) through the project "Fluxes of Radionuclides Emitted by the Phosphogypsum Piles Located at Huelva; Assessment of the Dispersion, Radiological Risks and Remediation Proposals" (Ref. CTM, 2015-68628-R)), the Regional Government of Andalusia project called "Basic processes regulating the fractionations and enrichments of natural radionuclides under acid mine drainage conditions" (Ref.: UHU-1255876), and the University of Cadiz project called "New methodogy of radioisotope isolation with environmental interest for its measurement by alpha spectrometry" (Ref: PR2019-024). Documen

“On the shoulders of giants” the history of women and men in Physics as a teaching innovation in Engineering degrees

This paper describes the results of the teaching innovation project. It was putting into practice at the School of Engineering of the University of Cádiz during the academic year 2016/2017. It was called "If I have seen further it is because I am sitting on the shoulders of giants. A little history of Women and Men in the history of Science and Engineering in the classrooms of the Higher School of Engineering". The main objective of the project was to inform the students of the first year of the Degrees of Electricity, Industrial Electronics, Industrial Technology, Aerospace, about the biographies and the contributions of some of the "giants" of the Physics and Engineering. It supposed a recovery of the History of the Physics in the teaching in the Degrees of Engineering. Moreover, we have tried to make visible some of these researches, especially, the feminine scientists. The realization of this project has increased the motivation of the students for the learning of physics. Knowing the biographies, contributions, successes and failures of great scientists, predisposes students to understand more complex concepts and, at the same time, taking those giants as a source of inspiration

Caracterización físico-química y radiactiva de los sub-productos provenientes de la industria de dióxido de titanio para su valorización en la industria del cemento: implicaciones radiológicas

El presente trabajo tiene como objetivo la caracterización físico-química y radiactiva, de las materias primas (ilmenita y slag), residuo (yeso rojo) y co-productos (caparrosa y monohidrato), procedentes de la industria de producción de dióxido de titanio. Para ello, se analizó su composición elemental (componentes mayoritarios y elementos trazas), así como su granulometría, mineralogía, composi-ción morfológica y contenido radiactivo. Esta caracterización pretende obtener información para las posibles aplicaciones del residuo y de los co-productos en diferentes campos como, construcción, ingeniería civil, etc.En particular, se han estudiado las propiedades más importantes de los cementos producidos con diferentes porcentajes de yeso rojo, comparando estas mezclas con un cemento Portland comercial (CEM).Se ha comprobado que además de cumplir todas las normas de calidad exigibles, tanto los niveles de lixiviación de elementos potencial-mente peligrosos, como los niveles de radiactividad presentes en los nuevos cementos obtenidos, son ambientalmente aceptables.The present study was conducted to characterize the raw materials (ilmenite and slag), waste (red gypsum) and several co-products (sulphate monohydrate and sulphate heptahydrated) from the titanium dioxide industry in relation to their elemental composition (major, minor and trace elements), granulometry, mineralogy, microscopic morphology, physical composition and radioactive content in order to apply this knowledge in the valorization of the co-products in fields such as construction, civil engineering, etc. In particular, the main properties of cements produced with different proportions of red gypsum were studied, and the obtained improvements, in relation to Ordinary Portland Cements (OPC), were evaluated.It was also demonstrated that the levels of pollutants and the radioactive content in the produced RG cements, remain within the regulated safety limits

Valorisation diagnosis of waste from the decontamination of phosphogypsum leachates through a combined calcium carbonate/hydroxide process

Phosphogypsum is an industrial waste considered as naturally occurring radioactive material. Stack disposal and exposure to the environmental condition involve the production of acid leachates with high potential pollutant loads as heavy metals and radionuclides. In this study, a sequential neutralisation process was applied for cleaning the generated releases, and the two obtained residues were characterised from the physical-chemical and radiological point of view before their valorisation. The cleaning process was made up of two steps: the first one using calcium carbonate until pH = 3.5, and the second one using calcium hydroxide until pH = 12. The residue obtained in the first step was mostly calcium fluoride, while in the second step most phosphates were precipitated, mainly as hydroxyapatite. The final liquid was treated to reduce pH lower than 9, which is the limit included in the current directive for discharges of liquid effluents into coastal waters. The main conclusion was that the solids from the first step could be valorised as an additive in the manufacture of commercial Portland cements and ceramics, while the solids from the second step could be used as raw material for the phosphoric acid manufacture.This research was funded by the following projects: Operative FEDER Program-Andalucía 2014–2020 (UHU-1255876, UHU-202020); Grants PID2020-116461RB-C21 and 116461RA-C22) funded by MICIU/AEI/10.13039/501100011033; Research grant UCA/REC44VPCT/2021, by the University of C´adiz; Andalusian government (I + D + i-JAPAIDI-Retos project PY20_00096); Grant TED2021-130361B–I00 funded by MICIU/AEI/10.13039/501100011033 and, by “European Union NextGenerationEU/PRTR”, and Campus de Excelencia Internacional del Mar (CEIMAR) (research project CEIJ-C07.2). The authors thank Fertiberia S.A. for their support in obtaining the water samples used in this study.Departamento de Física Aplicad