Pressing process and coloring property of baking-free bricks made of molybdenum tailing and cement

As a by-product of mining and the extensive production of industrial solid waste, tailing has many types, has a low utilization rate, and seriously affects the surrounding ecological environment. With the protection of natural resources and ecology in China, the traditional methods of obtaining clay and natural stone by mining cultivated land and preparing building materials by utilizing a high-temperature process will be avoided and eliminated gradually. In the face of the increasing demand for construction and decoration materials in the engineering construction sector in the Jing-Jin-Ji region, the use of tailing resources, which are stockpiled in large amounts in Chengde, Hebei Province, for the preparation of baking-free and decorative bricks is characterized by high usage of solid waste, low energy consumption, low environmental pollution, and considerable savings. In this study, for the simple system of molybdenum tailing-cement brick, the press molding process, microstructure, and coloring property after the addition of pigment were investigated. Results show that, for the baking-free brick, the appropriate cement-to-tailing ratio is 0.18~0.25, water-to-solid raw materials ratio for pressing is 0.10, pressing strength is 25 MPa, pressing holding time is 30 s, and brick performance is improved by the step-style pressing mode. After curing for a long time, the relative contents of Ca(OH)₂, ettringite, and CaCO₃ increase with the increase in the content of cement in the brick samples, whereas the content of mica decreases. If the mass content of cement reaches 25%, then the AFm phase (low sulfur calcium aluminum sulfate) will form. Large quantities of hydrated calcium silicate (C-S-H) gel, ettringite, and Ca(OH)₂ can also be observed in the brick samples. The addition of red, yellow, and green pigments of iron oxide type within 9% has only a slight effect on brick strength. By contrast, the addition of blue and black pigments causes strength loss. Thus, their contents should be appropriately controlled within 6% to 9%.