Application of phosphate tailings in building materials

Phosphate rock is a typical sedimentary rock that contains large amounts of phosphate minerals and is widely used in industries such as fertilizer manufacturing. According to the International Fertilizer Industry Association, China is the world's second-largest phosphate rock reserve. In recent years, the excessive use of phosphate rock has led to an increase in green gas and solid waste, which has become a major threat to the ecological environment.

It is a typical by-product of phosphate mining and flotation processes. Producing 1 ton of phosphate concentrate will produce 0.4 tons of phosphate tailings. my country accumulates nearly 9.5 million tons of phosphate tailings every year. However, only a limited number of them can be reused, with an efficiency of about 7%. The accumulation of phosphate tailings can bring heavy metals into the soil or water sources, threatening human health.

The main chemical components of phosphate rock tailings are considered to be silicon dioxide (SiO 2), magnesium oxide (MgO), iron oxide (Fe 2 O 3), phosphorus pentoxide (P 2 O 5), calcium oxide ( CaO) etc. As a result, phosphate tailings are often recycled into construction materials such as cement and ceramics. Adding phosphate tailings to the production of fired bricks can enhance their structural properties, and phosphate tailings can replace fine aggregates in cement concrete.

In addition, phosphate tailings content affects the setting time and heat of hydration properties of cement concrete. The increase in phosphate tailings content will prolong the setting time and reduce the heat of hydration. In addition, phosphate tailings are a suitable fertilizer resource because the silicon, phosphorus and calcium present in them are beneficial to agriculture.

In pavement engineering, industrial solid waste is processed into fine powder and then added directly to asphalt as a modifier or as a substitute for mineral powder. Generally speaking, the addition of inorganic powder as an additive or modifier will have excellent effects on improving the properties of asphalt such as fly ash, microsilica fume, and slag. Sharma improved the strength gain when using waste marble dust to replace sand and cement in concrete. However, the application of phosphate tailings in asphalt concrete has received limited attention.

Previous researchers have focused on phosphate sludge, another solid waste component of phosphates. Qian found that phosphate slag powder was alkaline and hydrophobic at high temperatures, which brought improvements to the anti-aging and anti-rutting properties of the original asphalt and the high-temperature stability and water resistance of the asphalt mixture. The results show that the phosphorus slag modified asphalt achieves the best high temperature stability and water stability at a dosage of 9%. SEM and FTIR results are consistent with mechanical properties where the addition of phosphate slag benefits road performance.