New Cadanav methodology for quantitative rock fall hazard assessment and zoning at the local scale

Rock fall hazard zoning is a challenging yet necessary task to be accomplished for planning an appropriate land use in mountainous areas. Methodologies currently adopted for elaborating zoning maps do not provide satisfactory results though, due to uncertainties and related assumptions characterising hazard assessment. The new Cadanav methodology, presented in this paper, aims at improving quantitative hazard assessment and zoning at the local scale, by reducing uncertainties mainly related to the technique for combining rock fall intensity and frequency of occurrence. Starting from available information on rock fall failure frequency and trajectory simulation results, the procedure merges in a strict way temporal frequency, probability of reach and energy data and evaluates the hazard degree by means of “hazard curves”. These curves are described at each point of the slope by a series of energy–return period couples representing the hazardous conditions which may possibly affect that location. The new Cadanav methodology is here detailed and compared to its original version. Hazard zoning results are illustrated along two different 2D slope profiles, for linear homogeneous cliff configurations, and according to the Swiss intensity–frequency diagram for rock fall hazard zoning. However, the procedure can be easily used with any other intensity–frequency diagram prescribed in national guidelines and, additionally, extended to problems involving 3D topographies.     

Gold recovery from a refractory pyrrhotite ore by biooxidation

The aim of the present investigation was to study the biooxidation of a refractory gold-bearing pyrrhotite, in order to increase the gold recovery during the subsequent conventional cyanidation.Bacterial cultures utilised in the biological test consisted predominantly of Thiobacillus genus. Tests were conducted at laboratory scale. The gold content of the ore sample, coming from Bolivia, was of 10 g t⁻¹ Au.After 24 h leaching time by direct cyanidation, low gold recovery was obtained (<20% Au), with a high reagent consumption. On the other hand, a high gold recovery was achieved for the biooxidated samples: after 24 h cyanidation gold dissolution reached about 91% Au.Experimental results have shown the technical feasibility of the biooxidative pretreatment prior to conventional leaching and a complete circuit of treatment, on laboratory scale, has been developed considering also the subsequent gold recovery by carbon adsorption/desorption and electrowinning.A gold extraction yield of about 86% was determined in the whole process for gold extraction from pyrrhotite (biooxidation, solid–liquid separation, cyanidation, adsorption, desorption, electrowinning).     

Selective zinc-lead extraction from chloride solutions with long-chain amines

The zinc-lead separation from a chloride solution in the form of a synthetic leach liquor has been studied using tertiary aliphatic amines and tetra-alkylammonium salts. Larger extractions, and hence distribution coefficients, are observed with ammonium salts. However, the best separation factors occur when employing tertiary amines. The results show that it is possible to leave the lead in the aqueous solution whilst the zinc is transferred to the organic phase by a proper choice of the hydrochloric acid and extractant concentrations. An approach to coordination chemistry is suitable to explain the extraction mechanism.     

Batch and semi-continuous tests in the bioleaching of manganiferous minerals by heterotrophic mixed microorganisms

In the present paper a study on bioleaching of manganiferous ores by heterotrophic mixed cultures is reported. The main goal of this work has been to study the bioreduction process of MnO₂ in lab-scale reactor and pilot plant tests, in order to investigate the process' pergormances in a scale larger than in shaken flasks. Lab-scale reactor tests were carried out in a batch and in a semi-continuous regime, monitoring manganese extraction yields and microbial growth. In the bioleaching tests 95–100% of manganese extraction (in 36–48 h of treatment using a content of pulp equal to 20% (w/v) of ore having a Mn grade of 17–20%) was obtained. Final tests in a pilot plant (V = 70L) were performed under non-sterilised conditions. From the experimental results a flowsheet of the process has been proposed. An approximate economical analysis of the bioleaching process has also been reported. The experimental results showed the technical feasibility of the process although several problems have to be resolved to allow for a full-scale application, such as the biomass disposal, the purification of the leach liquor before the final manganese recovery and the too high cost of the process.     

An evaluation of the performance of rock fall protection measures and their role in hazard zoning

Natural Hazards - Rock falls threaten human lives and assets in mountainous regions all over the world. Protection measures are one of the most effective solutions for mitigating rock fall-related...     

Extraction of uranium from heap leach liquor with tri-n-octylamine: Equilibrium data and flow-sheet calculations

The recovery of uranium from an acid heap leach liquor has been investigated. Tertiary amines (tri-n-octylamine) have been chosen as extractants because of their high selectivity and efficiency. According to the theory of the mechanism of extraction by amines, an equation has been proposed for the extraction isotherms of uranium. In amine extraction systems the organic-aqueous volume ratio is more important for uranium extraction efficiency than amine concentration. Equilibrium data are further developed according to the McCabe-Thiele approach to calculate from extraction isotherms and stripping isotherms the number of theoretical stages. Three stages and two stages respectively are predicted for extraction and stripping circuits with an over-all uranium recovery of 98.9%.     

Producing regionalism: regional movements, ecosystems and equity in a fast and slow growth region

Urban development pressures, preservation of environmentally sensitive areas and regional planning are the focus of current debates on regionalism in both fast and slow growth regions. Based on two cases—a campaign to preserve ecological integrity and reduce sprawl on the Oak Ridges Moraine in the Greater Toronto Area and Rochester’s anti-sprawl campaign for regional equity—the paper examines how two anti-sprawl campaigns brought to the fore alternative constructions of regionalism. In the fast growing Toronto region, citizen mobilization and upper tier intervention resulted in a legislative base for regionalism. In the slow growth Rochester region, the city had limited success in gaining regional redistribution. Such divergent outcomes relate to differences in intergovernmental relations, the city’s influence on the region, receptivity of suburbs to smart growth, and the potential for values of nature preservation and justice to mobilize regional coalitions.