THE SCORODITE PROCESS: A TECHNOLOGY FOR THE DISPOSAL OF ARSENIC IN THE 21ST CENTURY.

IN . (CASTRO S.H., F. AND SANCHE

Scorodite stability in mine drainage : Northern Portugal

Apresenta-se uma síntese de resultados procedentes de um programa alargado de reconhecimento de neoformações mineralógicas em rejeitos mineiros. Neste caso deu-se especial atenção às paragéneses secundárias em que a scorodite (FeAsO4·2H2O) é fase essencial, ocorrendo sob a forma de cristais isolados, agregados ou ainda em crustificações com diferentes estados de consolidação e níveis de compacidade. Foram selecionados espaços mineiros do N de Portugal, com depósitos hidrotermais de quartzo com sulfuretos metálicos: Castelhão, Argas-Cerquido, Tibães, Adoria e Penedono. Foram analisadas águas de efluente mineiro afetadas pela interação com escombreiras e escavações, e comparadas com águas do fundo regional de cada um dos espaços mineiros. Nos casos estudados, dependendo da interação água – mineral e na sequência da oxidação da arsenopirite, as águas de embebimento e escorrência seguem uma tendência definida até às condições de sobre-saturação e precipitação da scorodite, para um incremento de Eh e decréscimo de pH, a Eh>150 mV e [As] > 90ppb. Abstract:This work synthesizes some results of an extended program of recognition of minerals newly formed in mine wastes and diggings. In this case, it deals with the secondary paragenesis holding scorodite (FeAsO4 • 2H2O) as an essential species, occurring as isolated crystals, aggregates or crusts, with different degrees of consolidation and compaction. The selected mining sites, in Northern Portugal, corresponded to sulphide+quartz hydrothermal veins and mineralizations: Castelhão, Argas-Cerquido, Tibães, Adoria and Penedono. Mining effluents affected by the waste dumps, and the background water in each site were analysed. In the studied effluents, depending on the conditions of water-mineral interaction and arsenopirite oxidation, the composition of affected solutions follow a definite path, till de oversaturation and scorodite precipitation: increasing Eh /decreasing pH at Eh>150mV and As concentration higher than 90 ppb.This work synthesizes some results of an extended program of recognition of minerals newly formed in mine wastes and diggings. In this case, it deals with the secondary paragenesis holding scorodite (FeAsO4 • 2H2O) as an essential species, occurring as isolated crystals, aggregates or crusts, with different degrees of consolidation and compaction. The selected mining sites, in North-ern Portugal, corresponded to sulphide+quartz hydrothermal veins and mineralizations: Castelhão, Argas-Cerquido, Tibães, Adoria and Penedono. Mining effluents affected by the waste dumps, and the background water in each site were analysed. In the studied effluents, depending on the conditions of water-mineral interaction and arsenopirite oxidation, the composition of affected solutions follow a definite path, till de oversaturation and scorodite precipitation: increasing Eh / decreasing pH at Eh>150mV and As concentration higher than 90 ppb

Arsenic in the Water, Soil Bedrock, and Plants of the Ester Dome Area of Alaska

Concentrations of arsenic as large as 10 ppm (200 times the safe limit for drinking water) occur in the groundwater of a mineralized residential area near Fairbanks. Bedrock of the area contains 750 ppm As, primarily as arsenopyrite and scorodite. The oxygen-poor groundwater is enriched in As(III) and ferrous iron while the surface waters are iron free and contain less than 50 ppb As(V). Arsenic is removed from the water by coprecipitation with ferric hydroxide. Some iron-rich stream sediments contain as much as 1,400 ppm arsenic. The distribution of arsenic in the groundwater is controlled by the distribution of arsenic in the bedrock. The arsenic content of the B soil horizon over mineralized veins is about 150 ppm, while that over barren rock is 30 ppm. The vegetation over the veins is not significantly enriched in arsenic. Lettuce, radishes and tomatoes grown with arsenic-rich water (5 ppm) contain 16, 8 and 1 ppm As, respectively; these amounts are significantly greater than plants not treated with arsenic. Preliminary studies by state and federal health agencies show no detrimental effects on the health of persons drinking these arsenic-rich waters.The work upon which this publication is based was supported in part by funds provided by the Office of Water Research and Technology (Project B-037-ALAS, Agreement No. 14-34-0001-8056), U.S. Department of the Interior, Washington, D.C., as authorized by the Water Research and Development Act of 1978

Potential Impacts of Tailings and Tailings Cover Fertilization on Arsenic Mobility in Surface and Ground Waters

A number of mining sites worldwide, particularly gold mines, have tailings management facilities (TMFs) that contain high levels of arsenic. Current closed mine site regulatory agencies tend to prefer revegetation of TMFs as part of the mandated reclamation activities. At many sites, often in polar regions, vegetation is difficult to establish either directly on the tailings or on the coarse-rock covers due to nutrient poor soils, phytotoxicity problems, and/or a less than optimum climate. Addition of phosphorus-based fertilizers to the tailings and/or cover material is commonly considered in order to promote the revegetation process and – ideally – allow the site owners to discharge their closure duties as rapidly as possible. However, due to the similar geochemistry of arsenic and phosphorus oxyanion species, this type of mine closure strategy may have unintended consequences regarding arsenic mobility on and off the site. This document reviews the current state-of-the-art regarding mobilization of arsenic by phosphate ions, and identifies relevant risks and opportunities of using this information to better manage closed mine sites

Inventing Metallurgy in Western Eurasia: a Look Through the Microscope Lens

The quest for the ‘when’ and ‘where’ of the world's earliest metallurgy has been dominating scholarly research on this topic for decades. This paper looks beyond the question of origins by discussing ‘how’ and ‘why’ metallurgy was invented. It looks into choices and skills involved in selection, experimentation and processing of distinctively coloured copper minerals and ores throughout c. 2000 years in the Balkans. The body of evidence is built around the currently earliest evidence for copper smelting, dated at c. 5000 bc and discovered in the Serbian Vinča culture site of Belovode. The ‘microstructure’ of a metal invention process is explored through optical and compositional analyses of a selection of copper minerals and metal production evidence: ores, slags, slagged sherds and metal droplets recovered from seven settlements in Serbia and Bosnia and Herzegovina, altogether dated between the late seventh and the late fifth millennia bc. This research suggests an independent technological trajectory of the emergence of metallurgy in the Balkans based on a unique technological meme, black and green mineral, which follows the evolution of early metallurgy from mono- to polymetallic within the fifth millennium bc

Paint It Black: The Rise of Metallurgy in the Balkans

This paper integrates archaeological, material, microstructural and compositional data of c. 7,000 years old metallurgical production evidence with the aim to address the knowledge of the world’s earliest metalworkers. The main focus is placed on copper minerals, ores, slags, slagged sherds and metal droplets coming from four Vinča culture settlements in Serbia and Bosnia and Herzegovina: Belovode, Pločnik, Vinča and Gornja Tuzla, all dated between c. 5400 and 4400 BC. Chemical study of copper minerals throughout all sites points at striking uniformity in selecting black and green minerals from the early days of the settlements’ occupation, some of which predate the metal smelting events. Microstructural examination of metal production debris showed convincing technological similarity throughout c. six centuries of copper making in the studied sites, as well as a consistent choice of black and green ores for metal extraction. We argue that black and green ores were intentionally selected as ingredients for the metal smelting ‘recipe’ in the early stages of Balkan metallurgy based on the knowledge related to their characteristic visual aspects. This finding demonstrates how important the adequate combination of colours was for the early copper metalworkers and suggests a unique technological trajectory for the evolution of metallurgy in this part of the world. It also illustrates the capacity that micro-research carries in addressing the how and why of the emergence of metallurgy, and outlines a methodology for future studies of early metallurgies worldwide

A associação yanomamite-scorodite e a mineralização supergénica de In em detritos mineiros de zonas de cisalhamento com W-Au-As-Zn - Norte de Portugal

"Apresentado no VIII Congresso Nacional de Geologia 2010, Braga, 12-16 Julho"No âmbito de um programa de caracterização mineralógica de escombreiras, em sítios mineiros abandonados, detectou-se uma mineralização invulgar de índio (In) associada a detritos de grão grosseiro, provenientes de antigas lavras subterrâneas, em zonas de cisalhamento com W e/ou Au. A ocorrência mais significativa revela crescimento epitaxial de scorodite sobre núcleos de yanomamite, neoformados em cavidades de corrosão de sulfuretos em blocos soltos. O depósito primário, em Tibães (Braga), corresponde a veios hidrotermais em zonas de cisalhamento, com texturas do tipo fracturação-selagem (“crack-seal").Systematic characterization of waste dumps mineralogy in several abandoned mining sites allowed the detection of an unusual indium (In) mineralization associated with coarse grained debris from small scale underground workings in shear zones with W and/or Au. The most significant occurrence reveals epitaxic overgrowth of scorodite in transition to yanomamite cores, newly formed in corrosion cavities of sulphides in wasted boulders. Primary deposit is a hydrothermally veined and cracksealed shear zone in Tibães (Braga)

Avaliação do impacte da drenagem de água ácida na hidrogeoquímica do rio Zêzere : o caso de estudo da mina da Panasqueira, Portugal

A mineralização hidrotermal da Panasqueira localiza-se no centro de Portugal e é o maior depósito de Sn-W da Europa Ocidental. A exploração mineira e as operações do tratamento do minério deram origem a escombreiras de grandes dimensões, principalmente, nas áreas do Cabeço do Pião (escombreira do Rio) e Barroca Grande. A exploração e beneficiação dos processos de tratamento no local geraram rejeitados ricos em metais. A oxidação dos sulfuretos existentes na escombreira e o escoamento pela barragem de contenção de lixiviados, são os responsáveis pela mobilização e migração dos metais a partir dos rejeitados da mina até ao meio ambiente. As descargas das drenagens de água ácida da escombreira do Rio possuem um valor baixo de pH (pH < 3) e elevadas concentrações em metais pesados. No Rio Zêzere, o Fe e o As são os elementos que apresentam o mais rápido decaimento de teores uma vez que o As é adsorvido/e ou coprecipita e forma compostos pouco solúveis com os óxidos e hidróxidos de ferro. Em locais com baixo pH as espécies de Fe dissolvidas ocorrem, principalmente, como sulfatos complexos devido à elevada concentração de SO4 2-. Melanterite (Fe2+(SO4).7(H2O)) e pequenas quantidades de rozenite (Fe2+(SO4).4(H2O)) e szomolnokite (Fe2+(SO4).(H2O)) foram observadas na base da escombreira do Rio

Arsenic in mining environments: evidences from Sardinia (Italy)

In Sardinia, the dispersion of arsenic in the environment appears strictly linked with mineralised bodies and mining activities. Currently, the areas of main concern are the active gold mine at Furtei, and the abandoned Pb- As mine at Baccu Locci. At Furtei, the main sources of arsenic are enargite, and arsenian pyrite; an ongoing monitoring program of water quality in the area around the mine documented so far no major changes with respect to pre-mine conditions, except for the formation of extremely acid, As-rich pit lakes. At Baccu Locci, the main primary source is arsenopyrite; arsenic dispersion is essentially due to the past unwise practice of discarding mine tailings into the nearby creek. Arsenic is slowly released from residual arsenopyrite and temporary secondary mineral traps such as Fe-oxyhydroxides, causing contamination of soils and waters as far as 10 km downstream of the mine