The chemistry of semiconductor wafer processing liquid waste, contaminated by heavy metals, was investigated to determine arsenic content. Arsenic and gallium concentrations were determined for waste slurries collected from gallium arsenide (GaAs) wafer processing at three industrial sources and compared to slurries prepared under laboratory conditions. The arsenic and gallium content of waste slurries was analyzed using inductively coupled plasma mass-spectrometry (ICP-MS) and it is reported that the arsenic content of the waste streams was related to the wafer thinning process, with slurries from wafer polishing having the highest dissolved arsenic content at over 1,900 mgL(-1). Lapping slurries had much lower dissolved arsenic (< 90 mgL(-1)) content, but higher particulate contents. It is demonstrated that significant percentage of GaAs becomes soluble during wafer lapping. Grinding slurries had the lowest dissolved arsenic content at 15 mgL(-1). All three waste streams are classified as hazardous waste, based on their solids content and dissolved arsenic levels and treatment is required before discharge or disposal. It is calculated that as much as 93% of material is discarded through the entire GaAs device manufacturing process, with limited recycling. Although gallium can be economically recovered from waste slurries, there is little incentive to recover arsenic, which is mostly landfilled. Options for treating GaAs processing waste streams are reviewed and some recommendations made for handling the waste. Therefore, although the quantities of hazardous waste generated are miniscule in comparison to other industries, sustainable manufacturing practices are needed to minimize the environmental impact of GaAs semiconductor device fabrication.

This research study evaluated the effects of adding Scottish canal sediment after calcination at 750 °C in combination with GGBS on hydration, strength and microstructural properties in ternary cement mixtures in order to reduce their carbon footprint (CO2) and cost. A series of physico-chemical, hydration heat, mechanic performance, mercury porosity and microstructure tests or observations was performed in order to evaluate the fresh and hardened properties. The physical and chemical characterisation of the calcined sediments revealed good pozzolanic properties that could be valorised as a potential co-product in the cement industry. The results obtained for mortars with various percentages of calcined sediment confirmed that this represents a previously unrecognised potential source of high reactivity pozzolanic materials. The evolution of the compressive strength for the different types of mortars based on the partial substitution of cement by slag and calcined sediments showed a linear increase in compressive strength for 90 days. The best compressive strengths and porosity were observed in mortars composed of 50% cement, 40% slag and 10% calcined sediment (CSS10%) after 90 days. In conclusion, the addition of calcined canal sediments as an artificial pozzolanic material could improve strength and save significant amounts of energy or greenhouse gas emissions, while potentially contributing to Scotland’s ambitious 2045 net zero target and reducing greenhouse gas emissions by 2050 in the UK and Europe.

Purpose This paper presents a regionally downscaled economic model developed to assess the impacts of the management of dredged sediments on Gross Domestic Product (GDP) and jobs created; the model is validated and applied using real project data from sediment management projects in Ireland and Scotland. The model provides significant insight into and allows impact analysis for the economic aspect of sediment management projects with the potential to facilitate and inform stakeholders across the sediment management sector. Methods The economic model facilitates regional analysis of the impacts of sediment management projects on GDP and job creation for direct, indirect and induced effects. Methods for estimating the economic induced impacts are based on industry-specific type I and type II economic multipliers and coefficients, derived for the EU Interreg SURICATES partner countries (Ireland, Scotland, France and the Netherlands) using symmetric input–output tables and application of the open Leontief model and based on available economic data for the identified countries. The model is applied to sediment management projects in Ireland (a harbour development project at Castletownbere) and in Scotland (a bioremediation project at Falkirk). Model results are compared to project data for direct contribution to GDP and direct jobs created, and the model also estimates the indirect and induced economic project impacts. The model has been applied to undertake sensitivity analyses and compare different sediment management options. Results Model results provide a satisfactory comparison to real project data for direct cost and jobs created. Indirect economic benefits for GDP and employment created were estimated from 47 to 53% of direct impacts. The model has been applied to undertake sensitivity analyses and assess a range of different site-specific sediment management options with indirect economic impacts ranging from 42 to 53% of direct impacts. Conclusions The economic model results are compared to real project economic data, the validation exercise proving satisfactory with promising results. Sensitivity analyses and site-specific sediment management options have been assessed. The positive economic impacts of the Castletownbere Harbour project in particular are evident. These results highlight the potentially different economic impacts of the implementation of different sediment management options and in different regions and countries. The model allows the quantification of the economic benefits of sediment management projects. The model provides significant insight into and allows impact analysis for the economic aspect of sediment management projects and has the potential to facilitate and inform stakeholders and decision-makers across the sector.

Marmato, Colombia, has been an important centre of gold mining since before the first Spanish colonizers arrived in 1536. The Marmato deposit is hosted in a dacite and andesite porphyry stock as sheeted sulphide-rich veinlet systems. The district is currently experiencing a surge in both major mining projects and artisanal mining, driven by sustained high gold prices. Ore from small-scale and artisanal gold mining is processed in numerous small mills (entables) around Marmato, which impact surface water quality through the discharge of milled waste rock slurry, highly alkaline cyanide-treated effluent, and high dissolved metal loads. To investigate the impact of artisanal mining and ore processing, water samples were collected in January 2012 from streams around Marmato. The average dissolved metal concentrations in impacted streams were Zn, 78 mg L−1; Pb, 0.43 mg L−1; Cu, 403 µg L−1 Cd, 255 µg L−1; As, 235 µg L−1; Ni, 67 µg L−1; Co, 55 µg L−1; Sb, 7 µg L−1; and Hg, 42 ng L−1, exceeding World Health Organization drinking water guidelines. In addition, arsenic speciation was conducted in-situ and indicated that 91–95% of inorganic arsenic species is in the form of As(V). Spatial analysis of the data suggests that entables processing ore for artisanal miners are the main contributor to water pollution, with high sediment loads, alkalinity and elevated concentrations of dissolved arsenic, cadmium, mercury and lead, caused by the processing of gold-bearing sulphides in the entables. Geochemical data from surface water were compared to a comprehensive data set of whole rock analyses from drill core and channel samples from the deposit, indicating that the deposit is significantly enriched in gold, silver, lead, zinc, arsenic, antimony, and cadmium compared to crustal averages, which is reflected in the surface water geochemistry. However, elevated mercury levels in surface water cannot be explained by enrichment of mercury in the deposit and strongly suggest that mercury is being added to concentrates during ore processing to amalgamate fine gold.

The objective of this study is to assess the variation of pollution in the Thai-Laos Mekong associated with seasonal dynamics concomitant with the natural geological features and human activities that impact on the adverse quality of the river. The complex ecology of the 1500 km stretch of the Thai-Laos Mekong River has been studied in this paper to understand the relationship with the geomorphology, with the sub-tropical monsoonal climate and the impact of human activity. Sub-surface geology controls the nature and extent of the drainage basin and of the river channel. The volume flow of the river varies naturally and dynamically in phase with the rainfall; traditional models based on steady state hydraulics are inappropriate. Continuous erosion of the river banks and bed generates a sediment load of impure silt, mica, quartz and clay minerals that inhibits light penetration and limits the primary productivity of the river. The river separates two countries at different stages of development; it flows through or close to eight non-industrial conurbations (Populations 350,000-2,000,000) but is otherwise sparsely populated. The river is used for subsistence agriculture, village transport, fishing including aquaculture and as a source of domestic water. Hydroelectricity is generated from the Laos tributaries. The river is a depository for partially treated urban waste and untreated village waste, hence populations of E.coli bacteria sometimes render the water unsuitable for drinking unless treated with the highest value of 240/100 ml found at station 7 during the summer season of 2003. Furthermore the river is polluted by trace metals, notably cadmium and mercury, and by Polycyclic Aromatic Hydrocarbons (PAHs), which are particularly concentrated in the sediments. Previous work has shown that cadmium and mercury exceed the Probable Effect Level (PEL) values of Canadian Environmental Quality Guidelines and that the PAH concentrations were also greater than the Interim Sediment Quality Guidelines (ISQG). Consequently the fish stock, a vital source of protein for the local human population maybe seriously affected. As conflict between the demands of human activities will be exacerbated by the continuing development of the basin; monitoring must be continued and a better model of the river's ecology is needed to predict the impact of development.