Editorial for Special Issue “Gravity Concentration”

Gravity concentration is the process by which particles of different densities, sizes, and shapes separate from each other when under the action of gravity or centrifugal forces [...]

Study of gold-bearing ores material and mineralogical composition in Lower Angara region

In connection with the involvement in new deposits exploitation, represented by refractory oxidized ores with a fine-dispersed phase and valuable component low content, there have been trends in the processing of this type of raw material. The alluvial gold-bearing sands of Lower Angara region are of practical interest. The results of the material and mineralogical composition of gold-bearing ores made it possible to establish that most rock fragments are quartz-mica schists, which are dilapidated by weathering up to 15% of the sample mass and clay inclusions. Ore by 61.5% is presented with grain size of more than 20 mm. Gold is distributed almost evenly by size class. Basically, gold is found in intergrowths with quartz, mica, pyrite, and clay components. The size of the gold grains ranges from 0.03 to 0.05 mm to several microns. The content of the valuable component was about 3-5%. The result of gravity concentration of the original ores showed the possibility of obtaining gravity concentrates with a metal content of 220-250 g/t, with extraction up to 93-95% and obtaining tailings from 0.3-0.5 g/t, followed by leaching of cyanide and sulfur-alkaline solutions. The extraction of the valuable component into the solution was 80% and 98%, respectively. The results obtained indicate the possibility of processing these types of ores in Lower Angara region.

Characterization of amalgamation tailings from ASGM in Sekotong area, West Nusa Tenggara, Indonesia, and its potential added value

Artisanal and small-scale gold mining (ASGM) in Indonesia still uses mercury in amalgamation process to extract gold form the ores. The process easily produces gold but at the same time produces very dangerous mercury waste. In this study, a comprehensive series of tests were carried out on amalgamation tailings from the ASGM in Sekotong area, West Nusa Tenggara. The tailings contain mercury up to 150 ppm, above the safe threshold, and gold up to 20 ppm which is intended to be recovered. Furthermore, mineral liberation analysis (MLA) and gravity recoverable gold (GRG) test were performed to determine the feasibility of recovering gold from the tailings. The liberation degree of the gold started from particle size of 37 \xm causes challenging to recover it. However, the GRG test confirmed that the gold was still feasible to be recovered by gravity concentration.

Beneficiation of Faya Clay for Drilling Mud Production Using Froth Floatation and Jig Gravity Concentration Techniques

The comparative study for upgrading Faya clay, in Faya Town of Plateau State, Nigeria to oil and Gas drilling mud grade was carried out. The clay was sourced from three veins A, B, and C. The samples were homogenized, crushed and ground. 5 kg of the homogenized sample was used for the experiment and laboratory work. Chemical and mineralogical characterization of the clay sample was carried out using; X-ray fluorescence (XRF) and X-ray diffractorneter (XRD). The clay sample was beneficiated using two methods: froth flotation and gravity concentration method (Jigging). The chemical composition of the crude clay revealed that it contains 16.6% Al2O3, 35.6% SiO2, 0.559% K2O, 0.084% CaO, 6.133% Fe2O3, 0.91 % TiO2 and 38.7 % BaO. The result of XRD analysis shows that quartz is predominant in the sample with 61.7% wt quartz (SiO2). Other minerals found in the sample include 28.59% wt of dickite (Al2 Si205 (0H)), 8.89% wt goethite (Fe0 (0H 4) and 0.83% wt muscovite (KO.92 NaO.08) (Al.86 FeO.07 TiO.02) (Si.3 O.3 AlO.97) O10 (OH)2 at 2 . Froth flotation method is more efficient for the beneficiation of Faya clay as it improves the BaO composition of the clay from 38.7% to 52.2%, with a recovery of 97.2%, an enrichment and ratio of concentration of 1.4 compared with the jigging method, which improved BaO composition from 38.7% in the crude clay to 47.5%, with a recovery of 90.96% and an enrichment ratio of 0.7; and ratio of concentration of 0.7. Froth floatation improved the specific gravity of the clay from 3.3 to 4.31; while jigging improved the specific gravity from 3.3 to 4. 05. Therefore, froth flotation method is more appropriate for the concentration of Faya clay ahead of jigging method of processing.Keywords: Upgrading, Characterization, Faya - clay, Drilling, Production

Characterization of Demolished Concretes with Three Different Strengths for Recycling as Coarse Aggregate

This paper presents a physical characterization for the recycling into new concretes of three comminuted concretes: C16/20 (“ordinary concrete”), C50/60 (“high strength concrete”), and C70/85 (“very high strength concrete”). The top size of the crushed concretes was 19.1 mm and the size range was 4.75 to 19.1 mm. The characterization was carried out with coarse aggregate liberation, to be prepared and concentrated in a gravity concentration process. The density distribution of the coarse aggregate, cement paste, and sand was carried out in different size ranges (4.75/19.1 mm; 4.75/8.0 mm; 8.0/12.5 mm; and 12.5/19.1 mm) for the three concretes studied. The form factor of the samples, as well as the porosity determination of particles in different density ranges, are presented. The obtained results indicate that the coarse aggregate liberation was more intensive for the low resistance concrete (C16/20), but a reasonable coarse aggregate recovery is possible for all concretes.

Development of a combined processing technology for low-sulfide gold-bearing ores

This paper presents the results of laboratory dressability studies for low-sulfide gold-bearing ores using combined processing and subsequent oxidation leaching of the resulting combined concentrate. According to the current raw materials processing circuit used at the Sekisovskoye deposit, gravity concentration experiments were first carried out using the following laboratory equipment: a Knelson KSMD 3 centrifugal concentrator, an SKO-05 concentration table, and a two-chamber diaphragm jigging machine (i.e., OML by TsNIGRI). A significant portion (0.5 to 1.0 g/t) of the gold remains in the gravity concentration tailings. Subsequent flotation experiments for the tailings suggest that additional gold recovery is possible. The gold content in the final flotation tailings was in the range of 0.15–0.25 g/t. The final gold recovery in the combined process was therefore 93.7–96.5 %. The subsequent sorption cyanidation of the concentrate according to the current processing circuit allows depositing an average of 75.0–80.0 % Au on the coal. At the same time, the residual gold content in the sorption leaching tailings is significant and amounts to 3.6–7.5 g/t. The preliminary oxidation experiments for the concentrate slurry indicate the possibility of a more complete gold recovery with subsequent leaching, including sorption leaching. The residual gold content in the cakes was measured at 0.7–1.5 g/t, which ultimately yielded 95–96 % recovery at the leaching stage. The research was completed with the financial support of the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan under grant No. АР05130143.

Gravity Concentration in Artisanal Gold Mining

Worldwide there are over 43 million artisanal miners in virtually all developing countries extracting at least 30 different minerals. Gold, due to its increasing value, is the main mineral extracted by at least half of these miners. The large majority use amalgamation either as the final process to extract gold from gravity concentrates or from the whole ore. This latter method has been causing large losses of mercury to the environment and the most relevant world’s mercury pollution. For years, international agencies and researchers have been promoting gravity concentration methods as a way to eventually avoid the use of mercury or to reduce the mass of material to be amalgamated. This article reviews typical gravity concentration methods used by artisanal miners in developing countries, based on numerous field trips of the authors to more than 35 countries where artisanal gold mining is common.

BEHAVIOUR OF SULFUR, ARSENIC AND ORGANIC CARBON IN A GRAVITY CONCENTRATION OF GOLD FROM REFRACTORY ORE

The results of assay-gravimetric, chemical, mineralogical analyzes of gold ore are presented. According to the content of sulfide sulfur and the degree of oxidation of sulfur gold-bearing ore is assigned to the poor sulfide type of ore in the primary zone. Gold ore refers to refractory carbonaceous arsenic-containing sulfide ores. The gravity concentration of ore was assessed using a laboratory 3-inch Knelson KC-MD3 centrifugal concentrator. According to the results of the GRG test, the total gold extraction was 39.58% with the total concentrate yield of 3.96%. The extraction of gold in the first stage is lower than in the subsequent stages. This indicates the absence of large gold in the ore. The behavior of sulfur and arsenic during gravity concentration is similar to the behavior of gold. These data confirm that the main amount of gold is associated with arsenopyrite (arsenic pyrite) and pyrite. The behavior of organic carbon during gravity is significantly different. Only 3.39% of organic carbon passes into the gravity concentrate from ore, which reduces the persistence of the concentrate. Most of the organic carbon (96.61%) remains in the tails of gravity. The content of components in the total gravity concentrate was: Au 21.63 g/t, S 6.40%, As 0.82%, C(organic) 0.58%. The extraction of the components in the total concentrate is as follows, %: Au 39.58; S 34.52; As 27.27; C(organic) 3.39.