Métodos de Previsão da Geração de Ácido a Partir de Resíduos Mineiros

Os testes laboratoriais utilizados para determinar o potencial de geração de ácido podem ser de natureza estática ou dinâmica. Um teste estático determina simultaneamente, a partir de uma amostra, a capacidade total de geração de ácido bem como o potencial total de neutralização desse ácido. A capacidade total de geração de ácido é determinada ou como a diferença entre estes valores ou como o seu quociente. A partir desses resultados pretende-se inferir se existirá ou não geração de ácido quando da exposição dos resíduos aos agentes meteóricos. Estes testes não determinam a cinética da geração de ácido mas apenas o potencial de produção. Os testes estáticos são conduzidos de forma expedita e apresentam custos pouco relevantes. Os testes cinéticos pretendem simular, a uma velocidade acelerada, o que acontece nos locais mineiros. Exigem um tempo de realização superior e têm um custo superior. Os dados obtidos a partir destes testes podem ser utilizados para classificar os resíduos de acordo com o seu potencial de geração de ácido. Esta informação, quando recolhida e avaliada durante o próprio estudo de viabilidade de um novo empreendimento mineiro ou de construyção civil, permite projectar medidas de mitigação desde o início do projecto. A principal distinção operatória, a nível laboratorial, entre os dois tipos de testes reside no facto que os ensaios estáticos correspondem a uma única determinação temporal enquanto que os ensaios cinéticos recorrem a vários ciclos repetitivos de exposição da amostra a várias cargas de soluções aquosas. Os testes cinéticos permitem simultaneamente inferir a composição iónica dos lixiviados. De uma modo genérico pode-se afirmar que sob o ponto de vista metodológico os ensaios estáticos, devido à sua rapidez e baixo custo, podem ser efectuados com um grande número de amostras constituintes de várias unidades litológicas representativas, enquanto que os ensaios dinâmicos serão efectuados sobre uma ou duas amostras, geralmente compósitas e com uma composição sugerida pelos resultados obtidos com os testes estáticos. Os autores submeterem amostras dos resíduos do tratamento de minérios de duas explorações mineiras portuguesas em actividade a vários destes testes estáticos e dinâmicos, comparando-os entre si

A New Approach in the Design of Air Stripping Columns for the Treatment of Groundwater Contaminated With Volatile Organic Compounds

Volatile organic compounds are a common source of groundwater contamination that can be easily removed by air stripping in columns with random packing and using a counter-current flow between the phases. This work proposes a new methodology for column design for any type of packing and contaminant which avoids the necessity of an arbitrary chosen diameter. It also avoids the employment of the usual graphical Eckert correlations for pressure drop. The hydraulic features are previously chosen as a project criterion. The design procedure was translated into a convenient algorithm in C++ language. A column was built in order to test the design, the theoretical steady-state and dynamic behaviour. The experiments were conducted using a solution of chloroform in distilled water. The results allowed for a correction in the theoretical global mass transfer coefficient previously estimated by the Onda correlations, which depend on several parameters that are not easy to control in experiments. For best describe the column behaviour in stationary and dynamic conditions, an original mathematical model was developed. It consists in a system of two partial non linear differential equations (distributed parameters). Nevertheless, when flows are steady, the system became linear, although there is not an evident solution in analytical terms. In steady state the resulting ODE can be solved by analytical methods, and in dynamic state the discretization of the PDE by finite differences allows for the overcoming of this difficulty. To estimate the contaminant concentrations in both phases in the column, a numerical algorithm was used. The high number of resulting algebraic equations and the impossibility of generating a recursive procedure did not allow the construction of a generalized programme. But an iterative procedure developed in an electronic worksheet allowed for the simulation. The solution is stable only for similar discretizations values. If different values for time/space discretization parameters are used, the solution easily becomes unstable. The system dynamic behaviour was simulated for the common liquid phase perturbations: step, impulse, rectangular pulse and sinusoidal. The final results do not configure strange or non-predictable behaviours

Use of solvent extraction to remediate soils contaminated with hydrocarbons

The main objective of this research is to exploit the possibility of using an ex situ solvent extraction technique for the remediation of soils contaminated with semi-volatile petroleum hydrocarbons. The composition of the organic phase was chosen in order to form a single phase mixture with an aqueous phase and simultaneously not being disturbed (forming stable emulsions) by the soil particles hauling the contaminants. It should also permit a regeneration of the organic solvent phase. As first, we studied the miscibility domain of the chosen ternary systems constituted by ethyl acetate–acetone–water. This system proved to satisfy the previous requirements allowing for the formation of a single liquid phase mixture within a large spectrum of compositions, and also allowing for an intimate contact with the soil. Contaminants in the diesel range within different functional groups were selected: xylene, naphthalene and hexadecane. The analytical control was done by gas chromatography with FID detector. The kinetics of the extractions proved to be fast, leading to equilibrium after 10 min. The effect of the solid–liquid ratio on the extraction efficiency was studied. Lower S/L ratios (1:8, w/v) proved to be more efficient, reaching recoveries in the order of 95%. The option of extraction in multiple contacts did not improve the recovery in relation to a single contact. The solvent can be regenerated by distillation with a loss around 10%. The contaminants are not evaporated and they remain in the non-volatile phase. The global results show that the ex situ solvent extraction is technically a feasible option for the remediation of semi-volatile aromatic, polyaromatic and linear hydrocarbons

Nanoparticles for the remediation of agrogenic contaminated soil and groundwater – a review

The wide spread use and strong reliance on both fertilizers and pesticides made of agrigenic pollution one of the major contemporary threats to environment and human health. Impacts on the environment vary from local effects, such as eutrophycation1, 2, loss of biodiversity and diminished ecosystem health3, to global effects, such as the aggravation of global warming2, 4 and ozone layer depletion5. The novelty of nanoremediation and its early successes, reported for various contexts, present the prospect for the development of relevant applications for agrigenic contaminants

Nanoparticles based Permeable Reactive Barriers as an Eco-efficient Technology for nitrate remediation in soil and groundwater

The need to increase agricultural yield led, among others, to an increase in the consumption of nitrogen based fertilizers. As a consequence, there are excessive concentrations of nitrates, the most abundant of the reactive nitrogen (Nr) species, in several areas of the world. The demographic changes and projected population growth for the next decades, and the economic shifts which are already shaping the near future are powerful drivers for a further intensification in the use of fertilizers, with a predicted increase of the nitrogen loads in soils. Nitrate easily diffuses in the subsurface environments, portraying high mobility in soils. Moreover, the presence of high nitrate loads in water has the potential to cause an array of health dysfunctions, such as methemoglobinemia and several cancers. Permeable Reactive Barriers (PRB) placed strategically relatively to the nitrate source constitute an effective technology to tackle nitrate pollution. Ergo, PRB avoid various adverse impacts resulting from the displacement of reactive nitrogen downstream along water bodies. A four stages literature review was carried out in 34 databases. Initially, a set of pertinent key words were identified to perform the initial databases searches. Then, the synonyms of those initial key words were used to carry out a second set of databases searches. The third stage comprised the identification of other additional relevant terms from the research papers identified in the previous two stages. Again, databases searches were performed with this third set of key words. The final step consisted of the identification of relevant papers from the bibliography of the relevant papers identified in the previous three stages of the literature review process. The set of papers identified as relevant for in-depth analysis were assessed considering a set of relevant characterization variables

Permeable Reactive Barriers using nanoparticles to remediate nitrate pollution

Nitrat e (NO3 - ) i s per vasi ve i n t he bi ospher e[ 1, 2]. Cont emporar y agri cult ural pr acti ces are a mong t he maj or ant hr opogeni c sources of r eacti ve nitrogen speci es, wher e nitrat ei s t he most abundant of t hese [ 2]. Excessi ve a mount s of r eacti ve nitrogen i n soil s and gr oundwat er ar e creati ng si gnifi cant t hr eat s t o hu man healt h and saf et y [ 3] as well as a host of undesirabl e environment al i mpact s [ 2]; it i s curr ently consi der ed t he second most r el evant environment al i ssue, aft er car bon di oxide e mi ssi ons. Nowadays, a mong t he most r el evant and pr omi si ng appr oaches t o r educe nitrat e concentrati on i n wat er, na mel y gr oundwat er, ar e denitrifi cati on- based pr ocesses [ 4]. Per meabl e r eacti ve barri ers ( PRB) have been pr oven eff ecti ve i n r educi ng vari ous cont ami nant s i n copi ous a mount s, parti cul arl y i n shall ow gr oundwat er [ 5]. However t he possi bl e added eff ecti veness of usi ng nanoparti cl es i n t hese structur es t o obt ai n nitrogen gas from nitrat es requires f urt her i nvesti gati on

Parecer relativo ao valor patrimonial e estado de conservação do cavalete mineiro de S.Vicente das minas de carvão de S. Pedro da Cova Gondomar

Parecer solicitado e entregue à União das Freguesias Fânzeres e São Pedro da Cov

A systematic review of sustainable gold extraction from raw ores using alternative leaching reagents

ABSTRACT: Drawing on recent experimental and commercial developments, this review reappraises potential substitute leach reagents for cyanide in the gold mining sector. In addition to extraction, the application of these reagents in the gold processing, pre-treatment and gold purification stages is explored. The main objective here is to discuss how the gold extraction process can be more sustainable, with a view to developing more greener leaching reagents.info:eu-repo/semantics/publishedVersio

A case study undertaken recycling & reuse of glass fiber reinforced thermoset polumer wastes of composite materials industry

Glass fibre-reinforced plastics (GFRP) have been considered inherently difficult to recycle due to both: crosslinked nature of thermoset resins, which cannot be remoulded, and complex composition of the composite itself. Presently, most of the GFRP waste is landfilled leading to negative environmental impacts and supplementary added costs. With an increasing awareness of environmental matters and the subsequent desire to save resources, recycling would convert an expensive waste disposal into a profitable reusable material. In this study, efforts were made in order to recycle grinded GFRP waste, proceeding from pultrusion production scrap, into new and sustainable composite materials. For this purpose, GFRP waste recyclates, were incorporated into polyester based mortars as fine aggregate and filler replacements at different load contents and particle size distributions. Potential recycling solution was assessed by mechanical behaviour of resultant GFRP waste modified polymer mortars. Results revealed that GFRP waste filled polymer mortars present improved flexural and compressive behaviour over unmodified polyester based mortars, thus indicating the feasibility of the GFRP industrial waste reuse into concrete-polymer composite materials

Nitratos nos solos e águas subterrâneas – Perspectiva sobre a atualidade, tendências, implicações para a saúde ambiental e abordagens de redução de riscos

As práticas agrícolas contemporâneas encontram-se entre as principais fontes antropogénicas de nitrato. Concentrações elevadas de nitratos nos solos e lençóis de água provocam efeitos prejudiciais na saúde humana e criam desequilíbrios substantivos em diversos ecossistemas. De entre diversas abordagens de prevenção e controlo de poluição, as tecnologias de remediação apresentam uma relevância crescente, das quais se destaca as barreiras reativas permeáveis. O presente trabalho visa, no contexto das alterações introduzidas pelo crescimento sistemático das concentrações de nitrato em diversos ecossistemas, aquilatar os méritos e limitações relativas das barreiras reativas permeáveis e perspetivar possíveis vias de melhoria do desempenho. Para este efeito, foi conduzida uma pesquisa sistemática em diversas bases-de-dados segundo quatro etapas para identificar literatura relevante. É possível concluir que as barreiras reativas permeáveis constituem-se atualmente como uma tecnologia eficaz de desnitrificação, contudo não foram constatadas evidências da utilização de nanotecnologias para potenciar o desempenho nestes processos de desnitrificação