Composition of weathering crusts on sandstones from natural outcrops and architectonic elements in an urban environment

This work presents mineralogical and chemical characteristics of weathering crusts developed on sandstones exposed to various air pollution conditions. The samples have been collected from sandstone tors in the Carpathian Foothill and from buildings in Kraków. It has been stated that these crusts differ in both fabric and composition. The sandstone black crust from tors is rich in organic matter and composed of amorphous silica. Sulphate incrustations accompanied by dust particles have been only sometimes observed. Beneath the black crust, a zone coloured by iron (oxyhydr)oxides occurs. The enrichment of the surface crust in silica and iron compounds protects the rock interior from atmospheric impact. The sandstones from architectonic details are also covered by a thin carbon-rich black crust, but they are visibly loosened. Numerous salts, mainly gypsum and halite, crystallise here, thus enhancing deterioration of the rock. Moreover, spherical particles originated from industrial emissions are much more common. Gypsum in natural outcrops, forms isolated and well-developed crystals, whilst these found on the architectonic details are finer and densely cover the surface. Such diversity reflects various concentrations of acid air pollutants in solutions.     

Black layers on historical architecture

Background, aim and scope

The external surface of any building in urban polluted environment is unavoidably destined to be covered with layers that assume a grey to black colour and are generally called ‘black crusts’. These, according to standard protocols and glossary, are deteriorated surface layers of stone material; they can have variable thickness, are hard and fragile and can detach spontaneously from the substrate, which, in general, is quite decayed. Plain visual examination may lead to consider ‘black crusts’ all similar, whilst only a careful diagnostic investigation can distinguish ‘black crusts’ and the consequences of their formation on stone substrates. In this paper, various black layers on marble are studied and compared and the morphological and compositional characteristics discussed according to the related mechanisms of formation. Differences between old (hundred years) and recent crusts (30 years) are investigated and pointed out.

Materials and methods

Samples of black crusts collected from the Milan Cathedral façade (Candoglia Marble) have been studied and compared with the careful and synergic employ of traditional techniques: optical (transmission and reflected VIS light) and electron microscopy, X-ray spectrometry and micro-Fourier transform infrared spectroscopy.

Results

Visual examination of loose fragments does not allow to point out outstanding differences amongst the various samples; black layers have similar main mineral components, gypsum and airborne particles, with different spatial distribution. The microscopic studies allowed to point out the porosity differences, the gypsum crystallisation habit, different amount of embedded particles, level and progress of marble decay.

Discussion

The observations lead to define three main types of black crusts: black crust deriving from marble sulphation, compact deposit and encrustation due to exogenic materials deposition. Black crusts show evidence of sulphation in progress, without a clear continuity solution between crust and marble; the lack of separation is particularly evident in ‘recent’ crust, where the sulphation process is more active. Black compact deposits show a higher porosity than black crusts because gypsum is not coming from the chemical corrosion of the substrate but from outside; actually, in the former case, the substrate is sound. Encrustations show a highly regular crystal organisation of gypsum (close packed tabular crystals) that cannot be traced back to casual atmospheric deposit or to corrosion of the substrate but rather to the crystallisation of a solution coming from an external source. Also in this case, the marble is sound; evidence of the effect of some protection treatment is pointed out.

Conclusions

In spite of the apparent similarity of the examined samples, analytical results have evidenced three main types of black crusts: black crust with decayed substrate, compact deposit and black encrustation showing a sound substrate underneath. Experimental evidence of calcite grains sulphation in progress, taking place according to a model recently proposed, has been observed. Sulphation process is prevented where particular conservation treatments had been applied in the past.

Recommendations and perspectives

New experimental studies can be focussed to understand the specific conditions (measurements of micro-climatic and thermodynamic parameters) and mechanisms for black crusts formation in situ. The problem of the kinetic of the sulphation process of marble, the assessment of black layers formation in the case of different carbonate stone materials and the study of acid attack in presence of surface protecting layers deserve further investigation.     

Different decay patterns observed in a nineteenth-century building (Palma,Spain)

The effects of atmospheric pollutants and climatic conditions were studied in a decayed column in the Seminary of Sant Pere. This nineteenth-century building is situated in the historic centre of Palma (Mallorca, Spain), less than 0.5 km from the sea. Samples were collected from the internal and external part of the crusts formed in the four sides of the column. The samples were analysed by means of thermal analysis, X-ray diffractometry, scanning electron microscopy, Fourier transform infrared spectroscopy and ion chromatography. Results show significant differences in the four sides of the column. A high degree of carbonate stone sulfation is observed in all of the samples analysed. A synergistic effect between atmospheric factors and micropollutants on the deterioration of stone is observed. A high uptake of atmospheric particulate matter is found in the external part of the black crusts.     

Origin,characteristics and morphology of weathering crusts on Istria stone in Venice

To evaluate the effects of the environment on weathering of monuments of Istria stone in Venice, systematic mineralogical, petrographical and elemental analyses of depth profiles were performed on samples of surficial crusts (dendritic black, compact black, grey and white). Decay products of deposition and interactions between gases and stone, including wind blown dust, marine salts, anthropic aerosol, gypsum and nitrates, are incorporated into the mineral matrix down to a depth of 10 mm. In areas sheltered from rain, where black and grey crusts are observed, the high general humidity, carbonaceous particles and deposition of aerosols lead to the development of gypsum and other salts. In compact and grey crusts decay products decrease; in grey crusts carbonaceous particles are reduced, but in compact black crust products of previous treatments are found. In white crusts, formed in areas experiencing effective wash-out, chemical and mechanical attack cause surface recession.     

Application of laser ablation ICP-MS and traditional techniques to the study of black crusts on building stones: a new methodological approach

Introduction  

In this work, we propose an innovative application of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) as a methodological approach for the chemical characterisation of black crusts on stone monuments, associated with traditional micro-morphological (optical and scanning electron microscopy) and infrared spectroscopic techniques (FTIR).     

Air pollution records on selenite in the urban environment

Black crusts (BC) on selenite, i.e. gypsum stone used in buildings and monuments in the city of Bologna (northern Italy) have been studied.The crusts have been compared with genetically identical ones encountered on gypsum outcrops in the area surrounding the same city, in a relatively clean rural environment.Because of gypsum's high solubility, also in the past, BC began to form and embed particles of atmospheric aerosol as soon as the stone was used in construction, even though the SO₂ levels in the air were probably much lower than today. Unlike other types of stone (sandstone, limestone, marbles), selenite is currently undergoing a deceleration of dissolution processes, following the acidification of the environment caused by industrialisation. For this reason the BC on selenite are older (up to 580±45 yr), thicker (up to 4 cm) and far more stable than those encountered on other types of building stones used in the same area.The BC are stratified: at the base, in contact with the stone, the crust contains numerous prismatic black particles originating from wood combustion; immediately above the base layer these particles progressively increase; finally, in the outer part of the crust one encounters the characteristic black, spongy spherical fly-ash originating from the combustion of mineral oils.From the chemical point of view, a comparison between urban and rural crusts shows that elements such as C, Si, K, Fe, V, Cr, Ni, Zn, Ga, As and Pb are due to present-day and/or past pollutant sources within the city itself.Moreover, the chemical data from the stratigraphy of the BC show that, while C and K were more abundant in the past than now, elements such as Fe, V, Cr, (Mn, Ni), Cu, (Zn), (Ga), As, Pb characterise recent and current urban atmospheres.     

Embryonic sulphated black crusts on carbonate rocks in atmospheric simulation chamber and in the field: role of carbonaceous fly-ash

Experimental conditions characteristic of the urban pollution in many European cities over the last decades were reproduced in a simulation chamber in which samples of limestone were exposed for a period of 12 months, both naked or sprinkled with carbonaceous fly-ash. In agreement with the findings reported in the literature the fly-ash emitted by heavy fuel combustion are highly reactive, undergoing chemical and morphological transformations which give rise to crystals growth, especially gypsum. The development of gypsum crystals was observed overall in close proximity of fly-ash anchoring them to the limestone surface. Samples of the same limestone exposed in the field in a polluted environment for the same period of time led to similar results. The preliminary mechanisms leading to the genesis of sulphated black crusts in polluted environments were thus highlighted. Because of their roughness the embryonic black crusts increase the development of the crust by trapping new particles. This trapping is also facilitated by the wetness of the stone surface leading to the development of hydrated mineral (gypsum) in the water meniscus between fly-ash and stone surface.     

含锌离子模拟废水沉淀研究及污泥表征

采用氢氧化钙、碳酸钠和硫化钠处理含锌废水,在溶液pH、锌离子浓度、颗粒粒径、颗粒Zeta电位、上清液浊度和污泥体积等指标测定的基础上,结合沉淀产物表征,探讨了沉淀剂用量对锌离子去除率的影响及沉淀机理。研究结果表明,n(Ca(OH)2∶n(Zn)=1.5,去除率达到最大值99.65%,n(Na2CO3)∶n(Zn)=1.5,去除率达到最大值99.89%,n(Na2S)∶n(Zn)=2.5,去除率达到最大值99.95%。X-射线衍射和热重分析表明,氢氧化钙与废水生成的沉淀物为碳酸钙和氧化锌,碳酸钠与废水生成的沉淀物为氧化锌和碱式碳酸锌,硫化钠与废水生成的沉淀物为硫化锌,这对污泥处理处置以及回收利用有指导意义。     

The problem of sampling on built heritage: a preliminary study of a new non-invasive method

The relevance of a risk assessment of the built heritage was clearly justified due to the fact that it acts as a pollutant repository and hazardous pollutants have the capacity to penetrate into materials. However, the limitation of the sampling processes due to the high value of the built heritage makes a correct evaluation difficult. For that reason, in the present work, the potential of agar gels as non-invasive samplers of built heritage deterioration products, like crusts and patinas, was evaluated. Different gels of agar and Carbopol® (as control gel) were applied on these built surfaces considering several factors: the treatment time, the effectiveness of the addition of EDTA (ethylenediaminetetraacetic acid, C₁₀H₁₆N₂O₈) and its concentration and the use of a buffer at pH 7.5. All these factors were evaluated in order to determine the capacity of these gels as sampling systems under non-controlled atmospheric conditions. The results obtained in the assays were evaluated by visual examination, by evolution of pH and by the most important techniques used in the risk assessment analysis of the built heritage (Raman spectroscopy, scanning electron microscope (SEM)/energy dispersive X-ray (EDX) and inductively coupled plasma mass spectrometry (ICP-MS)). In this evaluation, the agar gels showed an intrinsic capacity as sampler with respect to the gel Carbopol® and thus, the best option between the studied gels consisted on agar gels with 2 % of EDTA and the longest application time. On the whole, the agar gels showed an interesting potential as non-invasive samplers of built heritage deterioration materials which should be studied more in depth.     

Ionic imbalance due to hydrogen carbonate from Asian dust

In an attempt to identify the ionic imbalance, hydrogen carbonate, HCO₃⁻ (bicarbonate), was determined together with the commonly determined nine major ions because the imbalance was frequently encountered in the chemical analysis of samples with high pHs. Titration method was applied for the determination of the samples with pH higher than 5.6. These samples amounted to 102 of the 1536 samples collected in Hokkaido, Northern Japan, from April 1998 to December 2002. Of the 102 samples, 74 (Group A) showed an acceptable ion balance without including HCO₃⁻. In the other 28 (Group B), however, inclusion of HCO₃⁻ successfully improved the ion balance. These results suggested that hydrogen carbonate was a potential candidate for explaining the imbalance. The hydrogen carbonate concentrations showed a strong correlation with the corresponding non-sea salt calcium (nss-Ca²⁺) concentrations, which implied that hydrogen carbonate was derived from calcium carbonate particles incorporated into falling raindrops or cloud droplets. For Group A, the relationship between hydrogen carbonate and the nss-calcium ion concentration was very similar to that for commonly suspended particles in Hokkaido. On the other hand, Group B exhibited a stronger but significantly different correlation. To the samples of Group B, a back-trajectory analysis was applied to demonstrate that the samples were associated with aerosol travelling from Northern China or Mongolia, which indicated that alkaline aerosol affected the chemistry. In consideration of these findings, the current standard of the ion balance should be critically reviewed for modification in regard to the contribution of hydrogen carbonate not only in source areas but also in receptor areas of alkaline aerosol.     

Size-differentiated chemical characteristics of Asian paleo dust: records from aeolian deposition on Chinese Loess Plateau

The Chinese Loess Plateau (CLP) receives and potentially contributes to Asian dust storms that affect particulate matter (PM) concentrations, visibility, and climate. Loess on the CLP has experienced little weathering effect and is regarded as an ideal record to represent geochemical characteristics of Asian paleo dust. Samples were taken from 2-, 9-, and 15-m depths (representing deposition periods from approximately 12,000 to approximately 200,000 yr ago) in the Xi Feng loess profile on the CLP. The samples were resuspended and then sampled through total suspended particulates (TSP), PM10, PM2.5, and PM1 (PM with aerodynamic diameters < approximately 30, 10, 2.5, and 1 microm, respectively) inlets onto filters for mass, elemental, ionic, and carbon analyses using a Desert Research Institute resuspension chamber. The elements Si, Ca, Al, Fe, K, Mg, water-soluble Ca (Ca2+), organic carbon, and carbonate carbon are the major constituents (> 1%) in loess among the four PM fractions (i.e., TSP, PM10, PM2.5, and PM1). Much of Ca is water soluble and corresponds with measures of carbonate, indicating that most of the calcium is in the form of calcium carbonate rather than other calcium minerals. Most of the K is insoluble, indicating that loess can be separated from biomass burning contributions when K+ is measured. The loess has elemental abundances similar to those of the upper continental crust (UCC) for Mg, Fe, Ti, Mn, V, Cr, and Ni, but substantially different ratios for other elements such as Ca, Co, Cu, As, and Pb. These suggest that the use of UCC as a reference to represent pure or paleo Asian dust needs to be further evaluated. The aerosol samples from the source regions have similar ratios to loess for crustal elements, but substantially different ratios for species from anthropogenic sources (e.g., K, P, V, Cr, Cu, Zn, Ni, and Pb), indicating that the aerosol samples from the geological-source-dominated environment are not a "pure" soil product as compared with loess.     

Environmental quality of Jordanian coastal surface sediment, Gulf of Aqaba, Red Sea

Surface sediment samples were collected from five stations along the Jordanian coast of the Gulf of Aqaba, Red Sea, during October and November over 2 years, 2000 and 2001. The monthly sedimentation rate also was estimated for the same stations. Collected sediments were analyzed for color, odor, redox potential, grain size, organic carbon, organic nitrogen, calcium carbonate, and total phosphorus. The Hotels area at the northernmost tip of the Gulf of Aqaba, characterized by sandy beaches and sea grass bottom habitat, exhibited the lowest values for redox potential and was associated with a black color. The Phosphate Port area exhibited the highest sedimentation rate, finest grain size, highest organic carbon content, and highest total phosphorus concentration. This is a deposition habitat that receives phosphate particles lost during shipment. The Marine Science Station and the Tourist Camp, typical coral reef habitats, had the highest calcium carbonate and organic nitrogen concentrations. This is directly attributed to the nature of the bottom habitat. Calcium carbonate deposits result from the erosion of hard corals, and organic nitrogen accumulates due to the rapid consumption and recycling of plankton in the coral reef framework. Comparison of the current records with old records from the 1970s and early 1980s indicates significant improvement in the environmental quality at the Phosphate Port. Tracking the coastal management practices over time shows that these improvements in the environmental quality can be attributed both to the zero discharge policy Jordan has followed since 1986 and to improvements in the phosphate handling system by the Ports Corporation.     

Wetting,deterioration and visual features of stone surfaces in an urban area

The deterioration of carbonaceous rocks in urban areas can be roughly classified in three kinds of feature patterns visibly distinguishable on the rock surface. In this paper the three different kinds of deterioration are described and interpreted in terms of the principal mechanisms leading to their formation. The way liquid water controls both the rate and the morphology of the deterioration crust formed on the stone as observed in the field, indicates that local rainfall is a critical factor in determining the type of deterioration. It appears that the different weathering observed actually depends on the way the interaction of rain with the surface occurs, at one extreme a complete washout of the surface, to the other where the surface is only very slightly wetted.The wetting resulting from moisture condensation on the stone surface appears to play a very minor role compared with that due to rainfall.     

Early stage of weathering of medieval-like potash–lime model glass: evaluation of key factors

Purpose  

Throughout history, a consequent part of the medieval stained glass windows have been lost, mostly because of deliberate or accidental mechanic destruction during war or revolution, but, in some cases, did not withstand the test of time simply because of their low durability. Indeed, the glasses that remain nowadays are for many in a poor state of conservation and are heavily deteriorated. Under general exposure conditions, stained glass windows undergo different kinds of weathering processes that modify their optical properties, chemistry, and structure: congruent dissolution, leaching, and particle deposition (the combination of those two leading together to the formation of neocrystallisations and eventually crusts). Previous research has studied the weathering forms and the mechanisms from which they are originated, some others identified the main environmental parameters responsible for the deterioration and highlighted that both intrinsic (glass composition) and extrinsic (environmental parameters) factors influence glass degradation. Nevertheless, a clear quantification of the impact of the different deterioration extrinsic factors has not been performed.     

Exploration of heterogeneous chemistry in model atmospheric particles using extended X-ray absorption fine structure analysis

As models of the composition and heterogeneous chemical reactions of the troposphere undergo refinement, novel application of state-of-the-art analytical techniques will be necessary to propound realistic characterizations of mineral dust chemistry. In this study, strontium carbonate particles treated with gaseous nitric acid and nitrogen dioxide were examined with X-ray absorption fine structure analysis (EXAFS). The X-ray spectra of carbonate and nitrate standards were fitted to ab initio calculations, which were used to determine the structure and consistency of strontium nitrate formed on strontium carbonate. By examining differences in mean square radial displacement and lattice spacing values obtained for bulk Sr(NO₃)₂ as compared to Sr(NO₃)₂ formed on SrCO₃, EXAFS proves effective as a tool for investigating the local structure and composition of heterogeneous aerosol particles. The implications of findings on reacted strontium carbonate for atmospheric models of calcium carbonate aerosol are discussed.     

Speciation of chromium in 12 agricultural soils from Turkey

The objective of the study was to speciate and to evaluate various soil Cr species in relation to soil properties. Surface soil samples were taken from outskirts of the Cr factory and applied a sequential extraction procedure. Extracts analyzed in atomic absorption spectrophotometry (AAS). Chromium was partitioned into exchangeable Cr, Cr bound to carbonate, Fe-Mn oxide, and organic matter, and residual Cr. The most common form of chromium was in the residual form, followed by the organic form. Very low concentrations of Cr were found in the exchangeable and carbonate forms. Mean values of the extractable forms of Cr, expressed in percentages of total soil contents were: 0.94% exchangeable, 0.80% carbonates, 2.13% oxides, 7.08% organics and 89.81% residual. Multiple regression analysis of analytical data revealed that soil pH, contents of organic matter and calcium carbonate were the most important factor controlling the distribution of Cr forms determined.     

The chemical and mineralogical behaviour of Pb in shooting range soils from central Sweden

Recently investigations have shown that the annual flux of lead from shotgun pellets to shooting range soils is significant in some countries. This paper presents the data of chemical and mineralogical analyses of soils and Pb-pellet crusts from five shooting ranges in Sweden and, based on these results, evaluates the retention of lead in these shooting range soils. In the soils, Pb-pellets and bullets are readily decomposed and transformed to crust materials composed of Pb-bearing minerals. The transformation products in the crust materials, identified by X-ray diffraction, are predominantly hydrocerussite [Pb(3)(CO(3))(2) (OH)(2)], associated with cerussite (PbCO(3)) and anglesite (PbSO(4)). In a period of 20-25 years, an average of 4.8% metallic lead in the pellets has been transformed to lead carbonate and lead sulphate, where the former is the more stable mineral in the surface environment. However, in soils relatively rich in humus an average of 15.6% metallic lead in the pellets was transformed to secondary lead compounds in the same period. The results of the chemical analyses indicate that Pb is rather immobile in the soil profile. The surficial horizon contains higher concentrations of lead (52-3400 mg kg(-1)), while lower concentrations of lead were found in the E and B horizons where the total Pb concentrations (8-37 mg kg(-1)) are within about one standard deviation of the mean reference sample concentration. An inverse relationship is revealed between the aluminium hydroxide content of the soil fraction and EDTA-extractable Pb, which suggests that these compounds have affected the retention of lead.     

Correlation between Calcium Carbonate Content and Emission Characteristics of Incense

Abstract

In Taiwan and China, calcium carbonate is commonly added as a filler during incense production to lower the cost. This study has found an unexpected benefit for this practice: it reduces particulate emission. Nine types of the popular incense on the local market were chosen for this study. The calcium content in raw material incense was analyzed by inductively coupled plasma atomic emission spectrometry, followed by X-ray diffraction (XRD) spectroscopy. The correlation between the calcium content and emission characteristics of incense was investigated. The calcium content varied from 1.8 to 60 mg/g (incense burned) among those nine different types of incense. Very little calcium (<1%) was found in natural wood or plants, which is mainly the raw material of incense. Instead, most calcium was artificially added in the form of CaCO₃ during manufacturing. The combustion characteristics, including burning rate, emission factors of particulate, ash, and solid-phase polycyclic aromatic hydrocarbons (SPAHs), varied significantly among the nine types of incense. Incense containing 2% calcium would emit 30% less S-PAHs, compared with those with little (<0.2%) calcium. More importantly, increasing the calcium content from 0.5 to 5% by adding CaCO₃ reduced the particulate emission from incense by ～50%.     

Neutralisation of an acidic pit lake by alkaline waste products

A former open pit where black shale (alum shale) was excavated during 1942–1965 has been water filled since 1966. The water chemistry was dominated by calcium and sulphate and had a pH of 3.2–3.4 until 1997–1998, when pH was gradually increasing. This was due to the intrusion of leachates from alkaline cement waste deposited close to the lake. A stable pH of around 7.5 was obtained after 6–7 years. The chemistry of the pit lake has changed due to the neutralisation. Concentrations of some dissolved metals, notably zinc and nickel, have gone down, as a result of adsorption/co-precipitation on solid phases (most likely iron and aluminium hydroxides), while other metals, notably uranium and molybdenum, are present at elevated levels. Uranium concentration is reaching a minimum of around pH 6.5 and is increasing at higher pH, which may indicate a formation of neutral and anionic uranyl carbonate species at high pH (and total carbonate levels around 1 mM). Weathering of the water-exposed shale is still in progress.     

不同Ca/P比下碳酸根对磷酸钙沉淀反应回收磷的影响

以模拟污水处理厂污泥厌氧消化液为处理对象,进行磷酸钙沉淀除磷小试实验,考察了不同Ca/P物质的量比下碳酸根(CO2-3)对磷酸钙沉淀反应回收磷的影响;利用扫描电镜(SEM)、X射线衍射仪(XRD)和傅里叶变换红外光谱(FTIR)对沉淀产物进行表征。结果表明,磷酸钙沉淀反应是一个快速过程,CO2-3的存在并未改变这一显著特征。磷酸钙沉淀反应过程中,CO2-3的存在降低了磷的去除率,改变了沉淀物形貌、结构和组分;实验设定范围内,磷酸钙的过饱和度越高,越难形成晶体态羟基磷灰石((Ca5(PO4)3OH,HAP);当pH值为9.0,Ca/P比为1.67时,CO2-3取代HAP晶格中的PO3-4,形成碳磷灰石(CHAP);当pH值为9.0,Ca/P比为3.33和5.01时,CO2-3和PO3-4之间竞争,形成碳酸钙(CaCO3);增大Ca/P能有效提高磷的去除率,降低CO2-3对磷酸钙沉淀反应的抑制作用,但综合考虑实际效果,选择Ca/P比为3.33作为适宜的反应条件。