Carina Ulsen

Chemical–mineralogical characterization of C&D waste recycled aggregates from São Paulo, Brazil

This study presents a methodology for the characterization of construction and demolition (C&D) waste recycled aggregates based on a combination of analytical techniques (X-ray fluorescence (XRF), soluble ions, semi-quantitative X-ray diffraction (XRD), thermogravimetric analysis (TGA-DTG) and hydrochloric acid (HCl) selective dissolution). These combined analytical techniques allow for the estimation of the amount of cement paste, its most important hydrated and carbonated phases, as well as the amount of clay and micas. Details of the methodology are presented here and the results of three representative C&D samples taken from the São Paulo region in Brazil are discussed. Chemical compositions of mixed C&D aggregate samples have mostly been influenced by particle size rather than the visual classification of C&D into red or grey and geographical origin. The amount of measured soluble salts in C&D aggregates (0.15-25.4mm) is lower than the usual limits for mortar and concrete production. The content of porous cement paste in the C&D aggregates is around 19.3% (w/w). However, this content is significantly lower than the 43% detected for the C&D powders (<0.15 mm). The clay content of the powders was also high, potentially resulting from soil intermixed with the C&D waste, as well as poorly burnt red ceramic. Since only about 50% of the measured CaO is combined with CO(2), the powders have potential use as raw materials for the cement industry.

Separability studies of construction and demolition waste recycled sand.

The quality of recycled aggregates from construction and demolition waste (CDW) is strictly related to the content of porous and low strength phases, and specifically to the patches of cement that remain attached to the surface of natural aggregates. This phase increases water absorption and compromises the consistency and strength of concrete made from recycled aggregates. Mineral processing has been applied to CDW recycling to remove the patches of adhered cement paste on coarse recycled aggregates. The recycled fine fraction is usually disregarded due to its high content of porous phases despite representing around 50% of the total waste. This paper focus on laboratory mineral separability studies for removing particles with a high content of cement paste from natural fine aggregate particles (quartz/feldspars). The procedure achieved processing of CDW by tertiary impact crushing to produce sand, followed by sieving and density and magnetic separability studies. The attained results confirmed that both methods were effective in reducing cement paste content and producing significant mass recovery (80% for density concentration and 60% for magnetic separation). The production of recycled sand contributes to the sustainability of the construction environment by reducing both the consumption of raw materials and disposal of CDW, particularly in large Brazilian centers with a low quantity of sand and increasing costs of this material due to long transportation distances.

Comminution and sizing processes of concrete block waste as recycled aggregates

Due to the environmental impact of construction and demolition waste (CDW), recycling is mandatory. It is also important that recycled concrete aggregates (RCA) are used in concrete to meet market demands. In the literature, the influence of RCAs on concrete has been investigated, but very limited studies have been conducted on how the origin of concrete waste and comminution processes influence RCA characteristics. This paper aims to investigate the influence of three different comminution and sizing processes (simple screening, crushing and grinding) on the composition, shape and porosity characteristics of RCA obtained from concrete block waste. Crushing and grinding implies a reduction of RCA porosity. However, due to the presence of coarse quartz rounded river pebbles in the original concrete block mixtures, the shape characteristics deteriorated. A large amount of powder (<0.15 mm) without detectable anhydrous cement was also generated.

Composição química de agregados mistos de resíduos de construção e demolição do Estado de São Paulo

Os Residuos de Construcao e Demolicao (RCDs) representam cerca de 50% dos residuos solidos de cidades brasileiras; a reciclagem e, portanto, desejavel, tanto do ponto de vista economico, como ambiental. Nesse trabalho sao apresentados resultados de estudos de caracterizacao quimica referentes a amostras de duas usinas de reciclagem do Estado de Sao Paulo. Verificou-se que a classificacao corrente do RCD, segundo criterios visuais (tipos cinza e vermelho), nao esta relacionada a composicao quimica destes, sendo esta influenciada, principalmente, pela granulometria. A composicao quimica dos RCDs varia em funcao dos conteudos de pasta de cimento, tipos dos agregados naturais (areia quartzosa ou granito), cerâmica vermelha e argila. Ainda, para a reciclagem dos residuos como agregados para concretos, sao necessarios dois estagios de britagem para atendimento as normas ABNT. A fracao miuda apresenta um enriquecimento nos teores de silica, indicando liberacao da pasta de cimento para os finos (< 0,15 mm). Os finos tem aplicacoes potenciais na industria de cimento.

Separação óptica do material cerâmico dos agregados mistos de resíduos de construção e demolição

A remocao de residuos de cerâmica vermelha dos agregados mistos procedentes de residuos de construcao e demolicao (RCD) deve ser priorizada para este material possa ser utilizado para a confeccao de concreto. Isso pode ser realizado por meio de diferentes tecnicas de processamento mineral, com principios de separacao, eficiencia, custos e impactos ambientais distintos. A principal vantagem da separacao optica e o uso reduzido de agua ou energia quando comparado com outros processos industriais. Este artigo tem por objetivo analisar os produtos obtidos por separacao optica de RCD mistos, com foco na remocao da cerâmica vermelha e conseguinte reducao da porosidade dos agregados reciclados para uso em concreto. A remocao da cerâmica vermelha viabiliza a obtencao de um agregado reciclado essencialmente composto de concreto, com menor porosidade e cuja absorcao de agua varia entre 4% e 7%. No Brasil, teores de ate 5% de cerâmica vermelha sao esperados no produto (agregado triado), e a producao de concretos de 20 a 30 MPa torna-se viavel com esse material.

Copper ore type definition from Sossego Mine using X-ray diffraction and cluster analysis technique

This paper presents the classification of 110 copper ore samples from Sossego Mine, based on X-ray diffraction and cluster analysis. The comparison based on the position and the intensity of the diffracted peaks allowed the distinction of seven ore types, whose differences refer to the proportion of major minerals: quartz, feldspar, actinolite, iron oxides, mica and chlorite. There was a strong correlation between the grouping and the location of the samples in Sequeirinho and Sossego orebodies. This relationship is due to different types and intensities of hydrothermal alteration prevailing in each body, which reflect the mineralogical composition and thus the X-ray diffractograms of samples.

Microstructural Characterization of Fine Recycled Aggregates by Sem-Mla

Construction and demolition wastes represent a significant amount of total municipal solid waste (in many cases, more than 50%). Their composition is basically of mineral origin (around 90% of the weight) and liable to be recycled through mineral processing. For a long time, the fine fraction has been disregarded or used as road base pavement, despite representing 50% of the weight. However recent studies have shown that this fraction are not that different from the coarse fractions and can be improved with the appropriate processing. The main difficulty in the production of high quality recycled aggregates is related to the presence of cement paste from previous constructions still adhered to the aggregates. This is responsible for increasing the porosity of recycled aggregates and diminishing their mechanical properties, such as durability, elasticity and resistance to compression. Therefore, the characterization and quantification of this phase is fundamental for guiding mineral processing, though there are few established procedures. The scope of this study involved the technological characterization of fine aggregates produced from construction and demolition waste with the intention of assessing the associations and liberation of the main phases. The experiment involved heavy liquid separations, chemical and mineralogical analyses, and scanning electron microscopy mineral liberation analysis (SEM-MLA) image analysis. The mineralogical characterization by X-ray diffraction (XRD) indicates that the main phases are tectosilicates (mainly quartz and feldspar), carbonates and phyllosilicates. The results of heavy liquid separation demonstrates the potential density separation and encourage further mineral processing to obtain a fine recycled aggregate with less cement paste content. The composition of the attained products is strictly related to the density of the separation; cement paste tends to concentrate in light products while quartz, feldspar, carbonates and mafic minerals are associated with denser products. The presence of carbonates in product d > 2.64 demonstrates that the determination of cement paste content by CaO+LOI overestimates this phase. The average partition of Ca revealed that just 77% is associated with the cement paste. The removal of porous particles on light products enables the accomplishment of a product with 76% of the total weight, about 80% of the total content of silica, alumina, iron oxide, Na2O+K2O and just 46% of the total CaO+LOI. According to quantitative image analysis, d > 2.5 presents a low content of cement paste and a total content of mineral phases (quartz, feldspar, mafic minerals and others) greater than 90%. The occurrence of phases with no cement paste attached (“mineral particles”) progressively increases in denser products. The products below 2.5 g/cm3 present up to 30% of particles free of cement paste while this proportion increases to around 90–95% in products sink at 2.6 g/cm3.

Assessment and Characterization of REE Minerals from an Alkali-Carbonatitic Complex

The demand for rare earth elements (REE) in high technology industries has been intensified and coupled with the fact that China accounts for about 95 % of world production and is actually creating trade restrictions for these elements; the search for new resources has been encouraged in several countries. This chapter presents a methodology for characterizing an earth rare mineralized sample, which occurs in association with alkali-carbonated complexes and with fine-grained monazite. The procedure was conducted by an automated image analysis system, besides physical separations and selective comminution by scrubbing, thereby evaluating the possibility of enrichment of rare earth bearing minerals in the attained products. Monazite is the main REE bearing mineral, counting for 40 % of the total content; it usually occurs in aggregates with micrometric crystals often with cerianite intergrowth. Monazite is mostly associated with anatase and Fe-oxy-hydroxides presenting a very poor liberation (34 wt% on average for material grinded below 0.30 mm). Both mineral separations and selective grinding by scrubbing did not succeed to obtain products with significant enrichment in REE.

Gold Characterization by MLA and Technological Tests: Discussion of Sample Preparation and Results

Gold has been present throughout the history of mankind and used to make jewelry and coins, and recently, it is put into use in industry. The price of gold in international market had a significant increase, surpassing 100 % in the last 5 years. Thereby, deposits with low levels of gold content as well as gold with complex associations or in a very fine particle size became exploitable again, allowing new projects and expansion of existing ones. However, as maximum process efficiency is indispensable and deep knowledge of the characteristics of these minerals and their behavior in face of beneficiation processes. Consequently, an accurate routine for mineralogical and technological characterization is essential. This chapter presents a methodology for characterizing low-grade ores with fine-grained gold. The procedure was conducted in three different samples from different regions, mineralogical assemblages, and grades.

Imputation of reactive silica and available alumina in bauxites by self-organizing maps

Geochemical analyses can provide multiple analytical variables. Accordingly, the generation of large geochemical databases enables imputation studies or analytical estimates of missing values or complex measuring. The processing of bauxite is a key step in the production of aluminum, in which the determination of Reactive Silica (RxSiO<inf>2</inf>) and Available Alumina (AvAl<inf>2</inf>O<inf>3</inf>) are very relevant. The traditional analytical method for achieving RxSiO<inf>2</inf> has limitations associated with poor repeatability and reproducibility of results. Based on the values from the unsupervised Self-Organizing Maps technique, this study aims to develop, systematically, the imputation of missing grades of the geochemical composition of bauxite samples of a database from three trial projects, for the variables: total Al<inf>2</inf>O<inf>3</inf>; total SiO<inf>2</inf>; total Fe<inf>2</inf>O<inf>3</inf>; and total TiO<inf>2</inf>. Each project was submitted to partial exclusion of AvAl<inf>2</inf>O<inf>3</inf> and RxSiO<inf>2</inf> values, in proportion of 20%, 30%, 40% and 50%, to investigate the SOM technique as imputation method for RxSiO<inf>2</inf> and AvAl<inf>2</inf>O<inf>3</inf>. By comparing the imputed values from the SOM analysis with the original values, SOM technique demonstrated to be an imputation tool capable of obtaining analytical results with up to 50% of missing data. Specifically, the best results demonstrate that AvAl<inf>2</inf>O<inf>3</inf> can be obtained by imputation with a higher correlation than RxSiO<inf>2</inf>, based on the parameters and variables involved in the study. Similarity in the nature of samples and an increase in the number of embedded analytical variables are factors that provided better imputation results.