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The effect of variations in the composition of kaolin and basalt on the geopolymer characteristics was carried out. The drying time was 4 h for cubic samples at 40, 50 and 60 °C and 9 h for cylindrical samples at 70 and 90 °C. The best geopolymer was 4 cylinder at 90 °C, which had a compressive strength of 8.075 MPa. The density of 2 cube geopolymer ranged as 26–1.94 g/cm3 at 60 °C. Silica–alumina compounds dominated the constituent compounds of geopolymer concrete, and the phases formed were quartz, anorthite and muscovite. [ABSTRACT FROM AUTHOR]

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Rare-earth metal is one of the critical elements because of its small amount with a lot of demand for this metal in a variety of the latest technologies, which are currently developed fast and intensively. The use of rare-earth metals can contribute to the development of innovations in the production of new materials in various fields, because these metals have strong, hard and heat-resistant properties. Rare-earth metals are found in complex compounds that makes it difficult to separate from ore. Obtaining of the rare-earth metals is realized by recycling the product from a secondary source of magnets containing rare-earth metals, such as NdFeB and SmCo magnets. Hydrometallurgical and pyrometallurgical processes can carry out the process of recovering of the rare-earth metals from secondary materials. There is a new research using bacteria as a rare-earth metal extractor to minimize environmental impact. Oxalic acid and other organic acids have potential in the recovery of rare-earth metals. As alternative, the rare-earth-free materials as candidates for permanent magnets are also mentioned. [ABSTRACT FROM AUTHOR]

Laterite nickel ore is a mineral rock, which contains iron–nickel oxide compounds. One processing technology proposed to treat the ore is the Caron process. In general, the Caron process combines pyrometallurgical and hydrometallurgical stages. In the pyrometallurgical step, the ore mixed with reductant is heated up to 1800 °C in a rotary kiln-electric furnace to transform iron–nickel oxide into iron–nickel alloy. In the hydrometallurgical stage, nickel has to be dissolved selectively using ammonia solution (alkaline). The further process is aimed to separate and purify the nickel in ammonia solution using solvent extraction and precipitation. The disadvantages of the pyrometallurgical stage in the Caron process include high-energy consumption, low economic value, and technical problems such as partially melted material, which hinders the further process. While in the hydrometallurgical stage, the extensive use of ammonia causes an environmental impact. Selective reduction is proposed to solve problems in the pyrometallurgical stage. Selective reduction is a process favouring the formation of iron oxide to obtain high nickel content in an intermediate product with less energy consumption. An additive is added to the ore to reduce selectively the nickel and decrease the reaction temperature. To solve the environmental impact of ammonia, a novel and safer chemical is proposed as a substitute — the monosodium glutamate (MSG). Selective reduction combined with alkaline leaching using MSG is proposed as an alternative to the Caron method. Precipitation is employed further to purify the nickel that results in nickel nanoparticles with 90–95 wt.% purity. [ABSTRACT FROM AUTHOR]

The effect of additional rolling in longitudinal and transverse directions on the microstructure, hardness and electrical conductivity of sheet aluminum alloy AA7075 (the Russian counterpart is alloy V95) is studied. It is shown that the rolling causes inhomogeneity of the microstructure and phase composition of the alloy in longitudinal and transverse directions but does not produce anisotropy of the hardness, which amounts to 96 HV in both directions. The electrical conductivity of the alloy after the pressure treatment depends substantially on the direction of the deformation and amounts to 78.6 and 92.8 S/cm in the transverse and longitudinal directions, respectively. At the same time, the post-rolling conductivity of alloy AA7075 remains high in both directions. [ABSTRACT FROM AUTHOR]

Hydrometallurgical extraction of nickel laterite is more efficient in terms of energy consumption, because it produces less exhaust gas compared to the pyrometallurgical method. Therefore, the hydrometallurgical method can increase the extraction yield of inferior nickel laterite more. In the calculation of the analysis of variance (ANOVA), three factors are used to determine the importance of the variables and the order of the most influential variables. ANOVA test is also a form of statistical hypothesis testing where we draw conclusions based on the inferential statistical data or groups. The ‘null’ hypothesis of the ANOVA test is that the data are simple random from the same population, so that they have the same expected mean and variance. In addition, a study of leaching kinetics is carried out using a shrink)ing core model to determine the reaction rate controller. The results show that the leaching time has an important role of acid, base, and monosodium glutamate in increasing the nickel extraction rate. Based on the ANOVA results, the two most influential factors are temperature and leaching time. The ANOVA-based calcula)tion use is more accurate than using a conventional method, such as ‘excel’, and it needs more development for mineral extraction in the future. [ABSTRACT FROM AUTHOR]