Distribution of As within Magnetic and Non-Magnetic Fractions of Fluidized-Bed Coal Combustion Ash

Separation of coal ash into magnetic and non-magnetic fractions facilitates their utilization when processed separately. Due to desulphurization additives added to coal during the fluidised-bed combustion, non-magnetic fractions often contain elevated CaO levels (while magnetic concentrates are typically rich in Fe2O3). Both CaO and Fe2O3 are known for their ability to bind As during the combustion, whose distribution is a crucial parameter in terms of proper utilization of these fractions. Therefore, the study deals with the As partitioning within magnetic and non-magnetic fractions of fluidized-bed coal combustion ashes. Two different (successive) procedures of dry magnetic separation were used to separate each ash into strongly magnetic, less magnetic, and a non-magnetic fraction. Due to their optimal utilization, the concentrations of As and other target elements in these fractions were evaluated and compared. Magnetic concentrates from the first separation step (in vibrofluidized state) contained 60–70% Fe2O3, magnetic concentrates separated manually out of the residues after the first separation contained 26–41% Fe2O3, and the non-magnetic residues contained 2.4–3.5% Fe2O3. Arsenic levels were the highest in the non-magnetic residues and gradually decreased with the increasing Fe2O3 content in the magnetic fractions. The dominant As association in the studied samples was to CaO (r = +0.909) and with SO3 (r = +0.906) whereas its joint occurrence with Fe2O3 was improbable (r = −0.834).

Analysis of the Effect of Dry Magnetic Separation on the Process of Ferruginous Quartzites Disintegration

The paper considers the results of the application of dry magnetic separation on samples of ferruginous quartzites of the Kostomuksha ore field, represented by refractory ore, free-milling ore, and their mixture. The assessment of the influence of the ore texture on the technological parameters of dry magnetic separation indicates their insignificant changes: the yield of the non-magnetic product varies from 12.4 to 13.5%, and the Fetotal content in the magnetic product increases by 1.11–1.14 times. A decrease of at least 15% in the number of harmful impurities was found: S by 16.2–17.3%, SiO2 by 15.5–21.1%, and Al2O3 by 39.1–48.4%. The authors have performed a comparative assessment of the granularity of the initial ore and the magnetic product with the measurement of energy consumption, as well as an analysis of the magnetite liberation on particle sizes of less than 2 mm. It was found that due to the release of a non-magnetic product in the amount of 12.3–14.5%, represented by non-magnetite or weakly mineralized rock varieties, energy consumption for the crushing process is reduced by at least 5%. The mineral liberation assessment showed that mainly free magnetite is contained in the −0.4 mm fineness class. It was found that in the magnetic separation product of the refractory ore sample, the amount of liberated magnetite in the size class −1 + 0 mm increases by 12.1% compared to the initial ore sample. For the free-milling ore sample, the opposite trend is observed: a decrease in the amount of free magnetite by 30.9% in the magnetic product. Analysis of the magnetite liberation in the mixture indicates deterioration in the results obtained during the separate crushing of refractory and free-milling ore and a decrease in the amount of liberated magnetite in the magnetic product by 60% compared to the initial ore.

Increasing of efficiency of dry magnetic enrichment of magnetite ore

A possibility of sintering ore obtaining from regular skarn magnetite ore by dry magnetic separation considered (DMS). A possibility of decreasing iron losses with DMS tails by additional control operation and application of separators of various design as well as application of screening studied. It was shown, that re-cleaning of intermediate product of –15+0 mm size enables to obtain from a regular skarn magnetite ore, a sintering ore having iron mass share more than 45% at the yield of 5.5% (of DMS intermediate product). It can be reached by application of a suspended belt separator with flat magnetic system. By using a drum separator with increased drum rotation speed, a DMS concentrate was obtained having iron mass share of 43.08%. Application of additional control operation of DMS tails enables to decrease the iron mass share in DMS tails from 11.25–11.32 to 9.97–10.67% as well as iron losses with DMS tails by 11.13–26.06% (rel.). To decrease the iron losses with DMS tails it is reasonable to increase magnetic field induction of drum separators of basic operation, but not apply additional control DMS operation. It was established, that the basic iron losses relate to fine class (–3+0 mm), characterized by increased iron mass share (14.43%). Therefore, for reextraction of iron from DMS tails a scheme with screening at 3 mm sieve and DMS of the mesh minus is possible. Such a scheme enables to obtain an intermediate product having iron mass share of 35.05–45.74% from DMS tails.

Influence of Mineralogy on the Dry Magnetic Separation of Ferruginous Manganese Ore—A Comparative Study

Magnetic separation is often considered pertinent for manganese ore beneficiation when the ore is abundant with siliceous rich gangue mineral phases. However, the process is deemed to be inapposite for the ferruginous type of ore, and remains a grey area of research. In the present investigation, two different types of manganese ore were studied in detail to understand the influence of mineralogy on their magnetic separation performance. Detailed experiments were performed by varying the critical variables of the dry magnetic separator, and the separation features were studied. The ore samples were thoroughly characterized by various techniques, including an automated advanced mineralogical tool. The mineralogical results revealed that primary manganese bearing minerals in both the ores are rich in cryptomelene, pyrolusite, psilomelane, and bixybyite. Similarly, the major gangue minerals were alumina-bearing minerals and iron-bearing phases (hematite and goethite). The optimum grade that could be obtained from single-stage dry magnetic separation was 35.52% Mn, and with a Mn:Fe ratio of 1.77, and 44% Mn recovery in the case of sample 1; whereas, a 33.75% Mn grade, with a Mn:Fe ratio of 1.66 at Mn recovery of 44% was reported for Sample 2. It was observed that both samples had a similar input chemistry (~28% Mn, ~1 Mn: Fe ratio) however, they had distinctive mineralogical assemblages. Furthermore, it was observed that the liberation of manganese mineral was in a course size range, i.e., 300 to 450 µm, while the association of iron and manganese bearing phases was lower in sample 1 when compared to sample 2.

Improvement of the technology for processing siderite ore from the Bakal deposit

The Urals is one of the unique iron ore provinces of the world, including all the variety of iron ores. Siderite ores are represented by the Bakal group of deposits, in which siderite in mineralogical terms is not a chemically pure iron carbonate, but has an isomorphic admixture of magnesium and calcium, forming sideroplesite and pistomesite. The main iron ore mineral of the siderite ore of this deposit is an isomorphic mixture of iron, magnesium and manganese carbonates, which occur in different quantitative ratios. A scheme for ore dressing is proposed, which includes crushing to a size of 10-0 mm and dry magnetic separation in a suspended state at a magnetic field strength of 52 k/m. The study of dry magnetic separation of siderite ore was carried out on a suspended separator with a constant magnetic field and on an electromagnetic separator 138T-SEM. The resulting magnetic fraction is sent to the baking, subsequent crushing to a size of 2-0 mm and dry magnetic separation in the suspended state. To increase the mass fraction of iron and reduce the mass fraction of magnesium oxide, the magnetic fraction is sent for grinding and wet magnetic separation. The results of the experiments have showed that the enrichment using high-intensity dry magnetic separation of siderite ore from various sections of the deposit, the mass fraction of MgO decreased from 9.4-12.3% to 8.0-10.1%, and the mass fraction of iron increased from 28.8-33.4% to 31.4-40.8%. As a result, a product with a mass fraction of iron 59.3-60.1% and magnesium oxide 10.0-11.3% has been obtained. The developed enrichment technology allows us to obtain conditioned raw materials, which can serve as a promising raw material for PJSC Magnitogorsk Iron and Steel Works (PJSC MMK)

Research of the influence of material composition and size of iron quartzites of the Olenegorsk deposit on the results of dry magnetic separation

On the example of a sample of ferruginous quartzites from the Olenegorskoye deposit, the possibility of preliminary concentration by dry magnetic separation (DMS) has been established. The mineralogical and petrographic studies have shown that, in terms of their textural and structural features and mineral composition, ferruginous quartzites may be divided into two types, differing in the amount of hematite included in their composition, which indicates the possibility of using DMS to generate the following three separation products: magnetite, hematite-magnetite, and rock. DMS with the use of a laboratory drum magnetic separator allowed selecting the upper size limit of 80 mm for lumps entering the separation. At the same time, 24.7 to 26.0 % of all waste and low-mineralized rocks with the mass fraction of Fetot of 4.51 to 6.07 % are transferred to the non-magnetic fraction during the separation of classes of –80+50 and –50+25 mm. For the size class of –25+10 mm, the yield and Fetot values are within the same limits. It has been shown that sulfidecontaining rocks and rocks of increased strength (with the strength coefficient of at least 23) are separated into the non-magnetic fraction. The strength of ferruginous quartzites does not exceed 20. This rock strength ratio confirms improved crushing and grinding efficiency. The possibility of separation of the magnetic fraction with the particle size of –80+25 mm into the following products has been established: the magnetite-hematite product (MF-1 + MF-2) with the mass fractions of Femagn 43.3% and Fehem 14.9 %, and the predominantly hematite product (MF-3 + MF-4) with the mass fractions of Femagn 1.1 % and Fehem 67.9 %.