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Abstract While F is an essential constituent of some rock-forming minerals such as fluorite and apatite, its major occurrence in the lithosphere is within hydroxysilicate minerals where F− occupies OH− lattice sites. The majority of the F occurring in the secondary environment derives from natural weathering processes with some soils derived from F-rich parent rocks containing over 1weight (wt) % F. Other natural sources of F are vulcanicity, wind-blown dust and a minor marine-derived component, with biomass burning, being in part natural, also a source. Several anthropogenic sources of environmental F have also been identified. Of the anthropogenic sources, the application of phosphate fertiliser, which probably adds over 2.3 Mt a−1 F to soils globally, represents the largest. While much of this is strongly retained in soils, in acidic some may be transferred to groundwater. In some abandoned mine sites in the UK where fluorite was associated with the mineralisation, soil F contents of up to 8 wt % have been recorded with plants growing on the sites containing up to 1wt % F. The rapid growth of urban areas in India, Pakistan and Bangladesh has resulted in an upsurge of brickmaking in Asia, with these 3 countries plus China accounting for over 75% of global brick production. As a result there is a large number of unregulated brick kilns which emit HF into the surrounding environment. Based on an annual global brick production of 1500 billion and the F contents of brick clays, it is estimated that about 1.8 Mt a−1 F are released to the environment from brick manufacture. This suggests that brickmaking is the largest source of atmospheric F emissions dwarfing that of coal combustion, 0.2–0.3 Mt a−1, phosphate fertiliser production, 0.07–0.10 Mt a−1, aluminium smelting, 0.041 Mt a−1, and even vulcanicity, 0.3–0.7 Mt a−1. However, it is apparent that atmospheric F emissions are not transported globally and as such their effects are manifested only in the local environment. Emissions from industry sited close to urban centres can impact these environments together with domestic coal combustion and the release of F from high octane fuels in motor vehicles. A more recent source of F in the environment stems from the large number of fluorocarbon compounds in everyday use. Degradation of some of these fluorocarbon compounds together with pyrolysis of fluoropolymers and burning of household refuse has resulted in the deposition of organofluorine compounds such trifluoroacetic acid in the environment. Highlights • The majority of the F occurring in the secondary environment derives from natural weathering processes. • The application of phosphate fertiliser is the largest anthropogenic source of F in the environment, probably adding over 2.3 Mt a−1 F to soils globally. • Global brick production is estimated to release about 1.8 Mt a−1 F, making it the largest source of F emissions to the atmosphere. • Other anthropogenic sources of F emissions to the atmosphere are coal combustion, 0.2–0.3 Mt a−1, phosphate fertiliser production, 0.07–0.10 Mt a−1 and aluminium smelting, 0.041 Mt a−1. • Vulcanicity has been estimated to release 0.3–0.7 Mt a−1to the atmosphere. [ABSTRACT FROM AUTHOR]

• Informal brick manufacturing in Bangladesh emits substantial air pollution. • People living downwind from brick kilns experience worse respiratory health when kilns are operating. • Effects are larger for women. • Banning kilns from being constructed nearby residential areas does not protect population health. • Brick manufacturing must be cleaner and more efficient to prevent this externality. Coal-fired brick kilns have spread rapidly in Bangladesh, where they are one of the largest sources of air pollution. The adverse health impacts of air pollution have been widely documented, yet there is little empirical evidence on the externalities of this important industry. We conducted a field study in Bangladesh to quantify the contribution of brick kilns to fine particulate matter (PM 2.5) and estimate the association with child asthma symptoms, chronic obstructive pulmonary disease (COPD), and general respiratory symptoms. We exploit variation in the timing of brick production, seasonal wind direction, and household proximity to kilns to isolate the effects of brick manufacturing from other sources of air pollution. We find that PM 2.5 is 72.3 μg/m3 (95% CI: 10.2, 134.3) higher in areas 2 km downwind from a brick kiln during the brick production season. We also find 2.2 (95% CI: 1.2, 4.3) greater odds of COPD symptoms among adults over 40 and 4.2 (95% CI: 2.7, 6.8) greater odds of respiratory symptoms among adults over 18. Among children under 5, we found greater odds of respiratory symptoms (2.1, 95% CI: 0.7, 6.0) and asthma symptoms (2.5, 95% CI: 0.1, 96.1), but the results were underpowered for the smaller sample of children. Our findings suggest that existing regulations, which require that kilns be at least 1–2 km from residential areas, schools, and health facilities, are inadequate to protect nearby communities from the substantial health burden brick manufacturing imposes. [ABSTRACT FROM AUTHOR]

This study investigated setting times and early age compressive strength of the high volume fly ash (HVFA) blended pastes prepared with ground materials. The pastes consisted of 60% Fly Ash + 30% Portland cement (CEM I) + 10% cement kiln dust (CKD) and tests were carried out for four different fly ashes. In phase 1, all the constituent binder materials (class F-fly ash, CEMI and CKD) were initially mixed in the relevant proportions and were ground for varying time periods (1, 2 and 4 h). In phase 2, the CEM I and CKD were mixed and ground for different time periods (1 and 2 h) and then added to the unground fly ash. Both wrapped and submerged curing were used for compressive strength test samples. Overall, grinding of constituents appeared to be largely ineffective at increasing 2 day compressive strength although strength enhancements at 28 days were generally observed. Paste samples that were made from interground constituents generally achieved higher 28 day strengths than corresponding pastes where only the activators were ground, although this was not consistent throughout so further investigation is suggested in this area. Submerged curing is generally less effective in increasing compressive strength than wrapped curing as leaching of CKD is suspected to have occurred. [ABSTRACT FROM AUTHOR]

Rotary kilns are well suited for processing woody biomass by torrefaction to produce bioenergy. One of the key issues for process design lies in the flow pattern modeling. The Saeman model is classically used to predict the mean residence time (MRT) and the bed depth profile of powder materials in rotary kilns. Its ability to describe wood chips flow arises. In the present study, residence time distribution (RTD) experiments are conducted with raw and torrefied wood chips. Effects of operating parameters - kiln slope, rotational speed and inlet flow-rate - on the average residence time, the variance and the mean solid hold-up are discussed. A plug flow with small extent of dispersion is emphasized, even if some segregation phenomena are highlighted. Torrefaction did not evidence any significant influence on the flow pattern. With a discrepancy of 20% between the measured and computed mean residence time, the predictive capacity of the classical Seaman model proved to be insufficient. The model is adapted to predict accurately the load profile and the mean residence time of particles with parallelepiped form. The discrepancy between experimental and calculated results is so reduced from 20% to 5% for the MRT and from 25% to 5% for the mean solid hold-up. [ABSTRACT FROM AUTHOR]

Two clayey raw materials collected in the Porto Ferro and Lago Baratz areas of Alghero in northwest Sardinia (Italy) were used to prepare handmade brick samples that were fired under oxidizing conditions at temperatures ranging between 750 and 1000°C to evaluate their possible use in the brickmaking industry. Both raw materials are rich in quartz and phyllosilicates but only the sample from Porto Ferro contains calcite. Granulometrically, the sample from Porto Ferro is a silty sand and shows higher plasticity than the clay from Lago Baratz which is classified as a sand. After firing, the samples acquire a red-orange colour and undergo significant mineralogical and textural changes. Phyllosilicate depletion is accompanied by the crystallisation of mullite and, only in Porto Ferro samples, the breakdown of calcite is followed by the formation of gehlenite, wollastonite and anorthite. Optical and electronic microscopic observations revealed that the temper grains are larger and more abundant in the bricks from Lago Baratz than in those from Porto Ferro. As firing temperature increased, pores became ellipsoidal in shape and the matrix became vitrified. The samples from Lago Baratz also show fissures at grain boundaries, which indicate the formation of an extensive network of pores and make these bricks very brittle when fired at low temperatures (750 and 800°C), so much so that hydric tests could not be performed on them. Bricks produced with the clayey material from Porto Ferro achieved the best results in terms of hydric behaviour, with a reduction in the water absorption capacity, and in terms of compactness, with an increase in ultrasound wave velocity. However, both Porto Ferro and Lago Baratz bricks behaved in similar ways when submitted to the salt crystallisation test, especially at 1000°C when a sufficient degree of vitrification was reached to ensure high quality samples. [ABSTRACT FROM AUTHOR]

The rapid urbanisation of many cities in south and south-east Asia has increased the demand for bricks, which are typically supplied from brick kilns in peri-urban areas. We report visible foliar damage to mango, apricot and plum trees in the vicinity of traditional Bull’s Trench brick kilns in Peshawar, Pakistan. Visible injury symptoms, hydrogen fluoride concentrations in air, and foliar fluoride concentrations were all greater in the vicinity of brick kilns than at more distant sites, indicating that fluoride emissions from brick kilns were the main cause of damage. Interviews with local farmers established the significant impact of this damage on their livelihoods. Since poorly regulated brick kilns are often found close to important peri-urban agricultural areas, we suggest that this may be a growing but unrecognised environmental problem in regions of Asia where emission control in brick kilns has not been improved. [Copyright &y& Elsevier]

Abstract: A new finding of the observation of an elemental gradient or zoning of calcium and sulphur in fired brick bodies is described, that does not appear to have been reported in the literature before. Many raw clays used in brickmaking and pottery contain sulphur and calcium evenly distributed in low amounts in the unfired clay body. However, when the clay body is fired in the kiln at 1050°C, the elements sulphur and calcium appear to combine to a compound, most probably calcium sulphate. The formation of calcium sulphate, visualised using energy dispersive imaging micro X-ray fluorescence (μ-XRF), only occurs around a so-called reduction core, also known as ‘black core’, caused by reduced magnetite Fe3O4 in the centre of the brick body. The presence of a black reduction core appears to cause the formation of a calcium sulphate layer around the black reduction core. This research contributes to the understanding of phenomena like salt formation, efflorescence and durability in solid clay brick bodies. Large sums are spent on building conservation by national economies and improvement of bricks is of key interest to them. [Copyright &y& Elsevier]

The granulometric, mineralogical, and geochemical features of two different types of clayey raw materials (carbonated clays, CC; and non-carbonated clays, NCC) used for the brickmaking industry near Zaragoza (Spain) have been studied. Their particle-size distribution suggests that they may be classified as silty clays and are suitable for use as thin-walled hollow bricks. For technological testing, prismatic bars obtained by extrusion under vacuum conditions from raw materials were fired from 800 to 1050 °C. Technological determinations, such as linear shrinkage, bulk density, hydric tests, and an accelerated decay test, indicate that both CC and NCC are suitable to be used as bricks for building, although bricks made of NCC would be of better quality. In addition, pore-size distribution suggests that the durability of the highest temperature fired products will be higher because of an increase both in the dominant pore access radius and in the percentage of larger pore sizes. [Copyright &y& Elsevier]

Two very different illitic–chloritic clays (calcareous and non-calcareous), both currently used in the Italian brickmaking industry, were used. Technological testing consisted in a simulation of the industrial processing performed at a laboratory scale. The pieces were obtained by three shaping techniques, pressing, extrusion and moulding, and fired at 1000 and 1100 °C, in fast and slow heating cycles. In each case their technological properties were studied. The microstructure and technological parameters of the ceramic pieces vary greatly, depending on the clay composition and the processing techniques. Pressing always produces pieces made from non-calcareous clay with the lowest drying and firing shrinkage, open porosity and water absorption. As it regards the calcareous clay, the lowest values of drying and firing shrinkage and water absorption are obtained by extrusion and moulding, respectively. The mechanical resistance, pore size distribution and critical pore diameter do not reflect clearly the influence of shaping techniques. Independently from the shaping technique adopted, all non-calcareous bodies show higher Maage''s indexes than the calcareous ones. In any case, the Maage''s durability factor is higher in extruded samples. [Copyright &y& Elsevier]