Green extraction of nickel and valuable metals from pyrrhotite samples with different crystallographic structures through acidophilic bioleaching.

Nowadays, due to the strategic status of nickel in the global market, utilizing its disregarded resources like low-grade nickel containing pyrrhotite is of significant importance. A comprehensive set of experiments and analyses were performed to determine the bioleaching capability and mechanism for nickel extraction from hexagonal and monoclinic pyrrhotite. Over 95% Ni extraction was achieved from the hexagonal pyrrhotite sample. Ni extraction from the monoclinic sample reached its maximum value of 67% and 90% at 3% pulp density, with mixed mesophilic and moderately thermophilic cultures, respectively. Characterization analyses indicated that jarosite and elemental sulfur formation in mixed mesophilic bioleaching reduced the samples' bio-oxidation rate and metal dissolution. The kinetics study revealed that the controlling step in thermophilic bioleaching is the chemical reaction; however, the mixed control model was best fitted on mesophilic data. Electrochemistry studies confirmed bioleaching results and indicated that monoclinic pyrrhotite's oxidation rate under the operating conditions is faster than hexagonal pyrrhotite, and the temperature positively correlates with the oxidation rate. Toxicity assessment analysis showed that the final residues of both bioleached samples could be considered environmentally safe.

Configuration of flowsheet and reagent dosage for gilsonite flotation towards the ultra-low-ash concentrate.

Gilsonite has a wide variety of applications in the industry, including the manufacture of electrodes, paints and resins, as well as the production of asphalt and roof-waterproofing material. Gilsonite ash is a determining parameter for its application in some industries (e.g., gilsonite with ash content < 5% used as an additive in drilling fluids, resins). Due to the shortage of high grade (low ash) gilsonite reserves, the aim of this study is to develop a processing flowsheet for the production of ultra-low-ash gilsonite (< 5%), based on process mineralogy studies and processing tests. For this purpose, mineralogical studies and flotation tests have been performed on a sample of gilsonite with an average ash content of 15%. According to mineralogical studies, carbonates and clay minerals are the main associated impurities (more than 90 vol.%). Furthermore, sulfur was observed in two forms of mineral (pyrite and marcasite) and organic in the structure of gilsonite. Most of these impurities are interlocked with gilsonite in size fractions smaller than 105 µm. The size fraction of + 105 - 420 µm has a higher pure gilsonite (approximately 90%) than other size fractions. By specifying the gangue minerals with gilsonite and the manner and extent of their interlocking with gilsonite, + 75 - 420 µm size fraction selected to perform flotation tests. Flotation tests were performed using different reagents including collector (Gas oil, Kerosene and Pine oil), frother (MIBC) and depressant (sodium silicate, tannic acid, sulfuric acid and sodium cyanide) in different dosages. Based on the results, the use of kerosene collector, MIBC frother and a mixture of sodium silicate, tannic acid, sulfuric acid and sodium cyanide depressant had the most favorable results in gilsonite flotation in the rougher stage. Cleaner and recleaner flotation stages for the rougher flotation concentrate resulted in a product with an ash content of 4.89%. Due to the interlocking of gilsonite with impurities in size fractions - 105 µm, it is better to re-grinding the concentrate of the rougher stage beforehand flotation in the cleaner and recleaner stages. Finally, based on the results of mineralogical studies and processing tests, a processing flowsheet including crushing and initial granulation of gilsonite, flotation in rougher, cleaner and recleaner stages has been proposed to produce gilsonite concentrate with < 5% ash content.

A process mineralogy approach to study the efficiency of milling of molybdenite circuit processing.

This study is conducted with the aim of investigating the efficiency of open and closed-circuit molybdenite ore comminution processes (primary and secondary mill, respectively), through mineralogical study of mills feed and product. For this purpose, particle size distribution, minerals distribution, degree of liberation and interlocking of minerals in mills feed and product were studied. According to the results, chalcopyrite, molybdenite, pyrite and covellite constitute the major part of the mineral composition of open-circuit mill feed. Minerals at the mill product, in the order of abundance include liberated molybdenite particles, liberated chalcopyrite and interlocked chalcopyrite with pyrite, liberated and interlocked pyrite particles, and associated silicate gangues. The d50 values of the feed and product particles of the open-circuit mill are equal to 13.80 and 13.40 microns, respectively. Degree of liberation of molybdenite for the feed and product of this mill is almost the same and is equal to 98.0%. Closed-circuit mill feed includes, in order of is abundance, liberated molybdenite particles in the form of blades and irregular polygonal shapes, liberated and interlocked chalcopyrite, and liberated and interlocked pyrite particles with gangue minerals. Molybdenite particles in the mill product are almost completely liberated, and the degree of liberation values of chalcopyrite and pyrite are 84.40% and 91.40%, respectively. According to particles size distribution of the feed (d50 equal to 25.03 microns) and the product (d50 equal to 24.24 microns) of closed-circuit mill, it can be stated that comminution is not well-operated in closed-circuit mill due to the low solid percentage of closed-circuit mill feed and the inefficiency of hydrocyclone. Examination of Mo, Cu, and Fe grade variations for 10 days in both off and on modes of mill shows that closed-circuit mill does not have an impact on comminution process. It can even be concluded that the mill has a destructive effect the flotation process by producing slimes.

Designing of an environmental assessment algorithm for surface mining projects.

This paper depicts the method used to quantify the environmental impact of mining activities in surface mine projects. The affected environment was broken down into thirteen components, such as Human health and immunity, Surface water, Air quality, etc. The effect of twenty impacting factors from the mining and milling activities was then calculated for each Environmental Component. Environmental assessments are often performed by using matrix methods in which one dimension of the matrix is the "Impacting Factor" and the other one is the "Environmental Components". For the presented matrix method, each Impacting Factor was first given a magnitude between -10 and 10. These factors are used to set up a matrix named Impacting Factor Matrix, whose elements represent the Impacting Factor values. The effects of each Impacting Factor on each Environmental Component were then quantified by multiplying the Impacting Factor Matrix by Weighting Factor Matrix. The elements of the weighting factors matrix reflect the effects of each Impacting Factor on each Environmental Component. The outlined method was originally developed for a mining and milling operation in Iran, but it can successfully be used for mining ventures and more general industrial activities in other countries in accordance to their environmental regulations and laws.