Encarnación Ruiz-Agudo

University of Granada | UGR · Department of Mineralogy and Petrology

El estudio de la formación de carbonato de calcio (CaCO3) ha demostrado que los procesos de nucleación y crecimiento no clásicos tienen un papel fundamental, en particular el carbonato de calcio amorfo (ACC). El crecimiento a partir de precursores amorfos se ha encontrado tanto en carbonato de calcio en biominerales, como en un número importante de...

Ancient Maya produced some of the most durable lime plasters on Earth, yet how this was achieved remains a secret. Here, we show that ancient Maya plasters from Copan (Honduras) include organics and have a calcite cement with meso-to-nanostructural features matching those of calcite biominerals (e.g., shells). To test the hypothesis that the organi...

The relatively recent development of nanolimes (i.e., alcoholic dispersions of Ca(OH)2 nanoparticles) has paved the way for new approaches to the conservation of important art works. Despite their many benefits, nanolimes have shown limited reactivity, back-migration, poor penetration, and lack of proper bonding to silicate substrates. In this work...

Hydration of anhydrous minerals such as periclase (MgO) is a common process during retrograde metamorphism (mainly serpentinization). During fluid-rock interactions, rock properties are altered by modified hydration reactions that change mineralogy (Kuleci et al. 2016). Similarly, the hydration of periclase is an important industrial reaction, espe...

The history of mineral components in cementitious materials begins with clays and bitumen in the most ancient mortars, followed by gypsum- and lime-based plasters, mortars, and concretes. Romans perfected the fabrication of extremely durable mortars that form the basis of audacious architectural monuments in Rome, massive harbor constructions, and...

Uno de los procesos de alteración más agresivos del material pétreo en el patrimonio arquitectónico es la cristalización de sales (Rodríguez-Navarro & Doehne, 1999). El origen de estas sales puede ser múltiple, incluyendo el uso de materiales de restauración y conservación incompatibles con los elementos de fábrica tradicional (Doehne & Price, 2010...

In this research, through the development of a teaching innovation project, the aim is to highlight the importance of educational and pedagogical changes that require both the adaptation of teaching to new situations and the possibility of taking advantage of the available resources to be applied in different degrees (master and degree) simultaneou...

Much stone sculptural and architectural heritage is crumbling, especially in intense tropical environments. This is exemplified by significant losses on carvings made of tuff stone at the Classic Maya site of Copan. Here we demonstrate that Copan stone primarily decays due to stress generated by humidity-related clay swelling resulting in spalling...

Weathering of primary silicate minerals under acidic conditions occurs in contexts as varied as acid mine drainage, volcanic environments, soils, stone monuments subjected to acid rain or Geological Carbon Storage (GCS). Considering the abundance of pyroxenes on the Earth crust, knowledge of their weathering kinetics and mechanisms may help to opti...

The advancement in analytical imaging techniques, including atomic force microscopy and scanning and transmission electron microscopies, has allowed us to observe processes occurring at mineral surfaces in situ at a nanoscale in real space and time, hence giving the possibility to elucidate reaction mechanisms. Classical crystal growth theories hav...

A novel synthesis route yields highly reactive nanobassanite with the largest surface area ever reported and with potential applications in biomedicine and heritage conservation.

The controlling factors and mechanisms of aqueous carbonation of primary silicates are still unclear. This precludes a better understanding of their chemical weathering in nature and is a strong handicap to implement effective Carbon Capture and Storage (CCS) strategies. Here, dissolution-carbonation reactions of two abundant Ca-Mg pyroxenes, augit...

In this work, calcium oxalate (CaOx) precursors were stabilized by poly(acrylic acid) (PAA) as an additive under in vitro crystallization assays involving the formation of pre-nucleation clusters of CaOx via a non-classical crystallization (NCC) pathway. The in vitro crystallization of CaOx was carried out in the presence of 10, 50 and 100 mg/L PAA...

To overcome the limitations of traditional conservation treatments used for protection and consolidation of stone and lime mortars and plasters, mostly based on polymers or alkoxysilanes, a novel treatment based on the activation of indigenous carbonatogenic bacteria has been recently proposed and applied both in the laboratory and in situ. Despite...

Coal-fired power plants are main contributors to atmospheric CO2 emissions. They also produce huge amounts of coal fly ash (CFA) waste, which is typically landfilled, posing significant environmental risks due to its high content of potentially toxic elements (PTE). However, CFA is an alkaline aluminosilicate-rich waste, which offers the possibilit...

In many systems prenucleation clusters (PNC), dense liquids and solid amorphous phases precede the formation of crystalline phases, which can grow via a nanoparticle aggregation mechanism. Despite intensive efforts, the current understanding on the mechanisms of such nonclassical crystallization processes is far from complete. Here by means of calc...

The weathering of building and sculptural stone due to increasing air pollution and salt damage results in the loss of invaluable cultural heritage artworks. This has prompted the design and application of novel and effective conservation treatments. Here, we study the effect of amorphous calcium carbonate (ACC) and oxalate (ACO) nanoparticles synt...

The kinetics of silicate carbonation in aqueous solutions are typically sluggish, especially at neutral to alkaline conditions. This hampers the complete understanding of the mechanisms and parameters that control mineral carbonation during carbon capture and storage (CCS). Here we study the hydrothermal dissolution and carbonation of pseudowollast...

Salt crystallization can produce severe damage in porous stones, with a dramatic impact on cultural heritage conservation. Such damage is related to the fact that repulsive forces arise between the salt crystals and the pore wall, generating a disjoining pressure that frequently exceeds the tensile strength of stone. In this paper, new treatments a...

One of the most promising strategies for the safe and permanent disposal of anthropogenic CO2 is its conversion into carbonate minerals via the carbonation of calcium and magnesium silicates. However, the mechanism of such a reaction is not well constrained, and its slow kinetics is a handicap for the implementation of silicate mineral carbonation...

Enhanced salt weathering resulting from global warming and increasing environmental pollution is endangering the survival of stone monuments and artworks. To mitigate the effects of these deleterious processes, numerous conservation treatments have been applied that, however, show limited efficacy. Here we present a novel, environmentally friendly,...

Although calcium oxalates are relevant biominerals, their formation mechanisms remain largely unresolved. Here, we investigate the early stages of calcium oxalate formation in pure and citrate-bearing solutions. Citrate is used as a well-known oxalate precipitation inhibitor; moreover, it resembles the functional domains of the biomolecules that mo...

Hydrated lime (Ca(OH)2) is a vernacular art and building material produced following slaking of CaO in water. If excess water is used, a slurry, called lime putty forms, which has been the preferred craftsman selection for formulating lime mortars since Roman times. A variety of natural additives were traditionally added to the lime putty to improv...

Recent experimental evidence and computer modeling have shown that the crystallization of a range of minerals does not necessarily follow classical models and theories. In several systems, liquid precursors, stable pre-nucleation clusters and amorphous phases precede the nucleation and growth of stable mineral phases. However, little is known on th...

Kinetics of reactions between minerals and solutions govern a wide range of natural and technological processes including weathering and soil formation, nutrient availability, biomineralization, acid mine-drainage, the fate of contaminants, or nuclear waste disposal. Theoretical and experimental studies performed in recent decades have changed our...

Cultural heritage objects and structures are subjected to a range of weathering processes that result in their decay and destruction. To slow weathering rates and/or mitigate their effects, several protective and consolidant materials have been used during conservation interventions. Treatments based on organic polymers and alkoxysilanes, as well a...

The precipitation of calcium carbonate, CaCO3 and the growth of calcite has been studied in aqueous solutions containing ferrous iron (Fe2+). Two different types of bulk experiments have been carried out: nucleation experiments at constant pH, following the procedure developed by Gebauer et al. (2008), revealed the stabilisation of aragonite induce...

In order to evaluate the organic phosphorus (OP) and pyrophosphate (PyroP) cycle and their fate in the environment, it is critical to understand the effects of mineral interfaces on the reactivity of adsorption and precipitation of OP and PyroP. Here, in situ atomic force microscopy (AFM) is used to directly observe the kinetics of coupled dissolut...

Naturally formed rims of calcium oxalates developed on calcareous stones have been recognized as effective protective coatings. Inspired in nature, it has been recently proposed the use of oxalate salts for the protection of stone surfaces via dissolution of the calcitic substrate and the subsequent precipitation of oxalate phases. In contrast, the...

Recent research has shown that biominerals and their biomimetics (i) typically form via an amorphous precursor phase, and (ii) commonly display a nanogranular texture. Apparently, these two key features are closely related, underlining the fact that the formation of biominerals and their biomimetics does not necessarily follow classical crystalliza...

The transformation of calcite into calcium sulphate phases in the presence of an aqueous phase is relevant to many technological processes, including remediation of acid mine drainage, exploitation of subsurface reservoirs, geological CO2 sequestration or the conservation of building stone. At acidic pH, the interaction of sulphate-bearing aqueous...

The mechanisms by which a commercial copolymer of maleic acid/allyl sulfonic acid with phosphonate groups (MASP), commonly used to mitigate or retard scale formation in the oil recovery industry, modifies the early precipitation stages of two common scale forming minerals, calcite and barite, have been investigated. MASP displays very similar effec...

A distinct nanogranular fine structure is shared by a wealth of biominerals from several species, classes and taxa. This nanoscopic organization affects the properties and behavior of the biogenic ceramic material and confers on them attributes that are essential to their function. We present a set of structure-relationship properties that are root...

The mechanism of surface coating formation (the so-called surface altered layers [SALs] or leached layers) during weathering of silicate minerals is controversial and hinges on understanding the saturation state of the fluid at the dissolving mineral surface. Here we present in-situ data on the evolution of the interfacial fluid composition during...

Nanolimes are alcohol dispersions of Ca(OH)2 nanoparticles used in the conservation of cultural heritage. Although it was believed that Ca(OH)2 particles were inert when dispersed in short-chain alcohols, it has been recently shown that they can undergo transformation into calcium alkoxides. Little is known, however, about the mechanism and kinetic...

Questions persist on the mechanisms of crystallization of sparingly soluble minerals such as calcium carbonate, calcium oxalate or barium sulphate. Compared to CaCO 3 , the mechanisms of nucleation and growth in the CaC2O4-H 2 O or BaSO4-H 2 O systems have received less attention. These phases are important due to their relevance as biominerals and...

The present work aims to evaluate the influence of pH, citrate and oxalic acid concentrations in calcium oxalate precipitation on calcite surfaces (Island Spar, Chihuahua, Mexico) through in-situ nanoscale observation using in situ atomic force microscopy (AFM, Multimode, Bruker) in flow-through experiments.

The precipitation of CaCO 3 and further growth of calcite has been studied in aqueous solutions containing ferrous iron (Fe 2+). Two different types of bulk experiments have been carried out. Nucleation experiments have been conducted at pH 9 with five different Ca T OT /Fe T OT ratios: 10, 5, 2.5, 1.25 and 0.625. As well, calcite growth experiment...

Barium sulphate (BaSO4) precipitation has been suggested to occur by non-classical pathways that include the formation of a dense liquid precursor phase, nucleation of primary nanoparticles and two levels of oriented aggregation resulting in micron-sized barite single crystals. In this study we build from this previous knowledge and explore how Ba2...

The formation of calcite (CaCO3), the most abundant carbonate mineral on Earth and a common biomineral, has been the focus of numerous studies. While recent research underlines the importance of nonclassical crystallization pathways involving amorphous precursors, direct evidence is lacking regarding the actual mechanism of calcite growth via an am...

Recent work has suggested that the rates of mineral dissolution in aqueous solutions are dependent on the kinetics of dehydration of the ions building the crystal. Dehydration kinetics will be ultimately determined by the competition between ion-water and water-water interactions, which can be significantly modified by the presence of background io...

Questions persist on the mechanisms of crystallization of sparingly soluble minerals such as calcium carbonate, calcium oxalate or barium sulphate. Compared to CaCO3, the mechanisms of nucleation and growth in the CaC2O4-H2O or BaSO4-H2O systems have received less attention. These phases are important due to their relevance as biominerals and/or un...

Esters of phosphoric acid constitute a large fraction of the total organic phosphorus (OP) in the soil environment and thus play an important role in the global phosphorus cycle. These esters, such as glucose-6-phosphate (G6P), exhibit unusual reactivity toward various mineral particles in soils, especially those containing calcite. Many important...

This study reports on the early stages of barite (BaSO4) precipitation from aqueous solution. TEM observations indicate that BaSO4 is formed by two levels of oriented aggregation of nanosized solid particles (nonclassical crystallization pathways). Oriented alignment of nanoparticles within micron-sized aggregates is observed, resulting in the form...

Arsenic dissolved in water represents a key environmental and health challenge because several million people are under the threat of contamination. In calcareous environments calcite may play an important role in arsenic solubility and transfer in water. Arsenic–calcite interactions remain controversial, especially for As(III) which was proposed t...

The reaction between diammonium hydrogen phosphate (DAP) and calcite in the stone to form hydroxyapatite (HAP) had provided a new product to consolidate limestone or Ca-rich stones, for example sandstones with carbonatic cement. However, what does it happen with the stones without Ca-bearing compounds? Obviously, HAP cannot form. In the other hand,...

The reaction between diammonium hydrogen phosphate (DAP) and calcite in the stone to form hydroxyapatite (HAP) had provided a new product to consolidate Ca-rich stones (limestone, marbles, sandstones). However, what does it happen with the stones without Ca-bearing compounds or, in the other hand, in Ca-rich stone was previously altered? Obviously,...

Knowledge of the dissolution behaviour of gypsum (CaSO4· 2H 2 O) in aqueous solutions is of primary importance in many natural and technological processes (Pachon-Rodriguez and Colombani, 2007), including the weathering of rocks and gypsum karst formations, deformation of gypsum-bearing rocks, the quality of drinking water, amelioration of soil aci...

Adsorption and subsequent immobilization of orthophosphate on iron oxides is of considerable importance in soil fertility and eutrophication studies. Here, in situ atomic force microscopy (AFM) has been used to probe the interaction of phosphate-bearing solutions with goethite, α-FeOOH, (010) cleavage surfaces. During the dissolution of goethite we...

Among the most relevant mineral replacement reactions are those involving sulphates and carbonates, which have important geological and technological implications. Here it is shown experimentally that during the interaction of calcite (CaCO3) cleavage surfaces with sulphate-bearing acidic solutions, calcite is ultimately replaced by gypsum (CaSO4·...

Atomic Force Microscopy (AFM) experiments show that barite (BaSO4) growth is influenced by the pH of the growth solution.•Growth and nucleation rates measured along the [100] crystallographic direction on the first layer grown on barite (001) natural surfaces increase at both high and low pH of the growth solutions•Growth from high pH solutions is...