Aluminum waste in alumina cement production (Mikhailovka)

Alumina cement is a rapidly hardening hydraulic binder containing low-basic calcium aluminates in the final product. The alumina cement production by melting is widespread. Melting of the mixture consisting of bauxite and limestone is carried out in the temperature range of 1500 to 1600 °C, which entails enormous energy consumption and, accordingly, the higher cost of resulting products. The paper studies the possibility of reducing the melting point as well as the cost of the main mixture component bauxite via its replacement by aluminum-containing waste.

Purpose: Suggest the dependence between the mixture composition and the Al2O3 content in the initial aluminum waste; determine the best annealing temperature for alumina clinker; study strength properties of the resulting alumina cement and the effect of introduced limestone on the main quality index.

Methodology: The chemical composition of the aluminum waste (sludge and powder), raw mixtures, and resulting clinker are detected in laboratory conditions using spectrophotometry and flame photometry methods in accordance with the state standard. X-ray phase analysis of waste and clinker is based on the powder diffraction method and conducted on the Thermo Scientific ARL X'TRA Powder Diffractometer. Physical and mechanical tests are carried out in accordance with the state standard poly-fraction sand.

Research findings: Laboratory studies show that aluminum waste (sludge and powder), consisting of gibbsite and boehmite in combination with limestone, is suitable for the production of alumina clinker. Depending on the initial Al2O3 content, their content in the raw mixture ranges from 60 to 75 %.

Value: Depending on the composition, the fest annealing temperature for alumina clinker, is 1350 to 1400 ℃; the mineralogical composition of clinkers consists of 85–90 % calcium aluminates. Alumina cement strength determined in small test samples having normal density and the ratio 1:0, is high after 2 days and ranges from 33.7 to 40.6 MPa. The addition of 5 % crystalline limestone into cement accelerates the initial rate of hardening and improves the strength from 33.7 to 53.2 MPa after 2 days due to the additional formation of 3CaO·Al2O3·CaCO3·11H2O.

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