Daniel Uliana

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.

Process Mineralogy of Lateritic Nickel Ore

This chapter presents a methodology for studying low-grade lateritic nickel ore, which usually presents complex mineralogy, with widespread nickel in several mineral phases. The study is focused on determining the mineralogy and the distribution of nickel in the bearing minerals. Laboratory assays comprise homogenization, sampling, and particle size analysis. Chemical analyses by X-ray fluorescence are performed in all fraction sizes, while mineralogical assessments by X-ray diffraction are carried out for the head samples. The mineralogical composition of the samples and the partition of main elements in the bearing minerals are assayed by size fraction through automated image analysis software (MLA) coupled with a scanning electron microscope (SEM). The chemical compositions of the several minerals identified in MLA are determined during systematic observations on SEM with energy-dispersive spectrometer (EDS).

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.