Validity of water industry wastes in cement industry

This paper examines the validity of several water industry wastes to be reused in different stages of cement production. The wastes considered are: a drinking water treatment plant sludge (DWTP), a sewage sludge (SS) and a spent activated carbon. Different procedures of drying of wastes using a novel dry spray system or subjected to thermal drying or stabilization and dried with lime are analysed. The spray drying process was successfully used with the DWTP sludge (but not with SS). The material was not found to be suitable as a supplementary material in blended cements. Despite this, the spray dried sludge did show good potential as partial or full substitute for clay as a raw material in cement clinker manufacture. A novel thermally drying process (Turbo-drying RINA-JET) was applied to produce dried sewage sludge. The dry sludge consisted of 56 % organic matter and has a high calorific value (8291 J / g), making it valid as an alternative fuel. The ash (35% of dry SS) contains Ca, Fe, P, Si and Al as main inorganic elements which are incorporated into the clinker phases. The burnability of the raw mixture containing this SS sludge was better than in the control raw mix. Furthermore, the paper describes an industrial process for stabilising sewage sludge (SS) with lime and evaluates the viability of the stabilised product, referred to as “Neutral”, as a raw material in the production of Portland cement clinker for the cement industry. The proposed process for sewage sludge treatment has a number of advantages over traditional treatments. In the Basic plant design, the chemical energy in the reagents generates sufficient thermal energy for the moisture to evaporate. This makes the process more energy-efficient than others. The validity of the “Neutral” product as a starting material in raw mixes for the production of cement clinker by substitution of limestone is demonstrated. Regarding the validity of spent activated carbon as an alternative to pet coke as fuel in Portland cement kilns, the carbon differed substantially from the coke, having lower calorific value (18 % less). However, the qualities of the spent coke were still sufficient for the intended use. The ash fraction of the spent activated carbon was mainly composed of anhydrite and quartz (SO3 = 14.1 %) and it is included into the clinker phases during the burning. The SO3 from the ashes promotes a very large growth in alite crystals in the clinker

Evaluation of a lime-mediated sewage sludge stabilisation process. Product characterisation and technological validation for its use in the cement industry

This paper describes an industrial process for stabilising sewage sludge (SS) with lime and evaluates the viability of the stabilised product, denominated Neutral, as a raw material for the cement industry. Lime not only stabilised the sludge, raised the temperature of the mix to 80-100 °C, furthering water evaporation, portlandite formation and the partial oxidation of the organic matter present in the sludge. Process mass and energy balances were determined. Neutral, a white powder consisting of portlandite (49.8%), calcite (16.6%), inorganic oxides (13.4%) and organic matter and moisture (20.2%), proved to be technologically apt for inclusion as a component in cement raw mixes. In this study, it was used instead of limestone in raw mixes clinkerised at 1400, 1450 and 1500 °C. These raw meals exhibited greater reactivity at high temperatures than the limestone product and their calcination at 1500 °C yielded clinker containing over 75% calcium silicates, the key phases in Portland clinker. Finally, the two types of raw meal (Neutral and limestone) were observed to exhibit similar mineralogy and crystal size and distribution. © 2011.Peer Reviewe

Activated carbon as an alternative fuel. Effect of carbon ash on cement clinkerization

9 págs.; 7 figs.; 10 tabs.Spent activated carbon is a by-product of potabilization plants. The present study explored the feasibility of valorizing this waste as an alternative fuel to replace oil coke in portland clinker furnaces. This involved determining its composition, calorific value, and ash and heavy metal content. Since the ash generated by spent activated carbon firing is taken up by the clinker, the possible effect of such uptake on clinkerization or the properties of the clinker obtained were also ascertained. Although spent activated carbon has an 18% lower calorific value than oil coke, one of the traditional cement kiln fuels, it was found to be apt for the purpose envisaged. Its ash content (10 wt%) is one order of magnitude higher than the ash content in coke. Spent activated carbon ash contains substantial proportions of anhydrite and quartz, hematite and augite, but consists primarily of amorphous matter (59 wt%). The effect of this ash on clinker phases was studied by clinkerizing raw meal in which it was used as a replacement for clay. Such meal exhibited high burnability and yielded clinkers with a composition and mineralogy comparable to the properties found in the industrial product. The sulfate present in the ash induced substantial alite crystal growth in the clinker. The loss of minority elements during clinkerization was likewise studied. © 2016 Elsevier Ltd. All rights reserved.This study was conducted under the leadership of Aguas de Barcelona as part of a CENIT 2007-1039 (National Strategic Consortia for Technical Research) project entitled “Technological development of a self-sustainable urban water cycle” (SOSTAQUA), funded by the Spanish Centre for Industrial Technological Development (CDTI). It has been also funded from BIA 2013-47876-C2-1-P and BIA2013- 43293-R projects.Peer Reviewe

In-situ reaction of the very early hydration of C3A-gypsum-sucrose system by Micro-Raman spectroscopy

6 págs.; 7 figs.; 3 tabs.; 1 app.This paper studied in situ, by Micro-Raman spectroscopy, the very early hydration of CA in the presence and absence of sulphates and with sucrose as an additive. For CA hydration in the absence of gypsum, when carbonation is not avoided, carbonate-AFm phases are formed, but in the presence of gypsum, hydroxi-AFm are the main phases. Ettringite is the AFm stable phase developed initially at 70 min of hydration with gypsum and no monosulphate is formed. In the presence of sucrose, this salt, instead of sulphate, is adsorbed over the surface of the CA, avoiding its reaction with sulphates until sucrose desorption. Three hours are necessary to lead to ettringite formation. A nucleation poisoning/adsorption surface mechanism is proposed for added sucrose systems. © 2016 Elsevier Ltd. All rights reserved.The authors wish to thanks the Geomateriales2 Program(S2013/ MIT-2914) supported by the Comunidad de Madrid and EU structural and cohesion funds (FSE and FEDER).Peer Reviewe

Sacrificial mortars for surface desalination

Four absorbent mortars were designed in this study and used as sacrificial desalinating media. The mortars comprised lime, sepiolite, nanosilica (72/3/25 by weight) and three admixtures (H2O2 and two commercial aerators) and had a liquid/solid ratio of 0.9, a mean porosity of 40% and a mean pore size of 0.8–0.7 μm. These mortars were applied three times to ashlars exhibiting surface saline efflorescence on a church at Talamanca del Jarama, a town in the Spanish province of Madrid. The salts impregnating the wall were characterised with XRD, FTIR and Micro-Raman spectroscopy. The ion concentrations in the ashlars was studied with ion chromatography at 0.5 cm, 1.5 cm and 3.0 cm from the surface after each application and the inner and outer surfaces of the mortars were analysed with Micro-Raman spectroscopy to determine the desalinating efficacy of the mortars. The mortars designed mobilised and absorbed the soluble salts in the ashlars; as a rule, elimination was most effective in anions with a smaller ionic volume and therefore greater ionic mobility and when the salt concentration was high and superficially located. Three years after application of the desalinating mortars, the salt concentration in the ashlars treated was 50% lower than prior to treatment.This study was funded by the Regional Government of Madrid’s ‘Geomateriales 2’ programme (S2013/MIT2914) under the CLIMORTEC project (BIA2014-53911-R).Peer reviewe

Effect of alkoxysilane on early age hydration in portland cement pastes

14 pags., 12 figs., 5 tabs.Silanes added during mortar or concrete preparation, may modify the fresh state properties, hydration kinetics and mechanical strength of the final product. The effects of silanes on cement hydration have been widely studied in the literature, however, there is some controversy about its effect at short ages. The present study was undertaken to determine the effect of a TEOS-based alkoxysilane (UCA-T), produced by ultrasound-assisted pre-hydrolysis of an oligomeric precursor, on early age cement paste hydration. The nature of the processes modifying the various stages of cement hydration kinetics in the presence of the alkoxysilane was ascertained by analysing paste composition at several ages (defined on the grounds of calorimetric curve results) using XRD, TG-DTG, FTIR and Raman spectroscopy. The calorimetric curve of pastes containing UCA-T exhibited a new early age, pre-induction period exothermal peak, indicative of UCA-T hydrolysis, C3A and C3S dissolution and ettringite and C–S–H gel precipitation. Portlandite, however, did not precipitate but reacts with the Si(OH)4 sourced from UCA-T hydrolysis to generate further C–S–H gel. The induction period following on that new exothermal peak was considerably longer than the period observed in the reference cement, an effect that intensified at higher UCA-T content.This study was funded by the European Union’s Horizon H2020 Research and Innovation Programme under Grant Agreement No. 760858. Funding was also received from the Regional Government of Madrid, (S2018/NMT-4372 TOP Heritage-CM Programme). The support received from the CSIC’s PTI-PAIS network during the roll-out of both projects is likewise gratefully acknowledged.Peer reviewe

Evaluation of a lime-mediated sewage sludge stabilisation process. Product characterisation and technological validation for its use in the cement industry

This paper describes an industrial process for stabilising sewage sludge (SS) with lime and evaluates the viability of the stabilised product, denominated Neutral, as a raw material for the cement industry. Lime not only stabilised the sludge, raised the temperature of the mix to 80–100 C, furthering water evaporation, portlandite formation and the partial oxidation of the organic matter present in the sludge. Process mass and energy balances were determined. Neutral, a white powder consisting of portlandite (49.8%), calcite (16.6%), inorganic oxides (13.4%) and organic matter and moisture (20.2%), proved to be technologically apt for inclusion as a component in cement raw mixes. In this study, it was used instead of limestone in raw mixes clinkerised at 1400, 1450 and 1500 C. These raw meals exhibited greater reactivity at high temperatures than the limestone product and their calcination at 1500 C yielded clinker containing over 75% calcium silicates, the key phases in Portland clinker. Finally, the two types of raw meal (Neutral and limestone) were observed to exhibit similar mineralogy and crystal size and distribution.Peer Reviewe

Evaluation of a lime-mediated sewage sludge stabilisation process. Product characterisation and technological validation for its use in the cement industry

This paper describes an industrial process for stabilising sewage sludge (SS) with lime and evaluates the viability of the stabilised product, denominated Neutral, as a raw material for the cement industry. Lime not only stabilised the sludge, raised the temperature of the mix to 80–100 C, furthering water evaporation, portlandite formation and the partial oxidation of the organic matter present in the sludge. Process mass and energy balances were determined. Neutral, a white powder consisting of portlandite (49.8%), calcite (16.6%), inorganic oxides (13.4%) and organic matter and moisture (20.2%), proved to be technologically apt for inclusion as a component in cement raw mixes. In this study, it was used instead of limestone in raw mixes clinkerised at 1400, 1450 and 1500 C. These raw meals exhibited greater reactivity at high temperatures than the limestone product and their calcination at 1500 C yielded clinker containing over 75% calcium silicates, the key phases in Portland clinker. Finally, the two types of raw meal (Neutral and limestone) were observed to exhibit similar mineralogy and crystal size and distribution.Peer Reviewe

Model for the Processing and Estimation of Dual Frequency Echo Sounder Observations in Detailed Bathymetries

The dataset acquired by an echo sounder generally comprises outliers and erroneous measurements which must be automatically processed. The main aim of this research is the development and validation of an algorithm which permits detecting outliers, estimating their real value from data acquired with a multifrequency echo sounder, and verifying the measure according to the desired accuracy. The process considers the nature of the seabed and improves the density and number of lectures without globally compromising the precision, but enhancing it in areas with anomalous measurements. Twenty-nine percent of this type of measurements, which would have been otherwise rejected, have been estimate