Chinese scientists target mineral powders and diatomite processing

By Albert Li
Published: Monday, 25 January 2016

CUMT developing surface modification technology, which aims to compensate for quality issues.

High value technical products, such as super-fine mineral powders and surface modification technologies, are among the priority areas being targeted by researchers in China as the country moves to enhance the value of its nonmetallic mineral industry, delegates at the China International High Tech Development Association Conference in Jian, Shandong province, heard in December.

Speaking at the conference, Shuilin Zheng, a professor in the field of nonmetallic minerals at the China University of Mining and Technology (CUMT), explained that the purpose of organically modifying the surface of inorganic powder is to increase the product’s function in applications like fillers, base materials and resins.

For example, it can increase the dispersity of inorganic filler in base materials and can be used in organic and inorganic composite materials such as plastic and rubber, paints and coatings, inorganic salt, fertilisers and extinguishing agents.

There are two ways of organically modifying the surface of inorganic powder – a dry method and a wet method.

The dry method involves dispersing powder in modification equipment while applying modification agents at controlled temperatures. This process is simple and can be applied using any modification agent, especially in physical and chemical coating modification of non-water soluble agents.

The wet method is applicable to water-soluble agents and has a better dispersity of surface modification agents and uniformity of surface coating, but requires drying afterwards.

Another technique under development, dubbed a "two-in-one technique" by Zheng, involves crushing prior to surface modification. Modifying agents are added when mineral ores are crushed, a step that can simplify the process and even increase crushing efficiency. However, the temperature is difficult to control, and high temperatures can damage the particle structure of the agents. Adding the agent at the right time to ensure it is fully dispersed through the crushed ore is also important.

An additional process of applying surface modification agents while powder is drying is also being tested, but because the temperature needed to dry the material is above 200°C, agents with a low boiling point will be evaporated, meaning that their function time is short.

Equipment needed for the surface modification of mineral powders includes high speed heating technology for the dry method and reaction kettles or temperature controlled reaction tanks for the wet process. Specialised "SLG-type" continuous equipment can also be used for powder surface modification.

News_9  

Chinese scientists are eager to showcase their research into producing higher
value materials from non-metallic minerals. 


Diatomite separation

CUMT is also seeking to advance the chemical method of separating diatomite from micron fine clay, as part of a drive to take greater advantage of China’s extensive diatomite resources.

Professor Zheng said that as the quality of Chinese diatomite trails that of the US, processing and purification are key to the effective development of the country’s reserves of the mineral.

Both the separation of diatomite from micron fine clays and the ventilation of nanometre pore paths are crucial in the processing of low grade diatomite.

As the physical method of processing the mineral cannot currently completely separate stagnated nano clay in the diatomite pore path, the chemical method must be used for high purity diatomite requirements, he explained.

The university it pursuing research into improving the chemical purification method as well as methods of recycling chemical agents and waste fluids.

China is home to 70 active diatomite mines with proven reserves of 400m tonnes and prospective reserves of over 2bn tonnes, according to Zheng. Of this, Jilin province contains more than half, at 210m tonnes proven; Yunnan province contains 82m tonnes; and Zhejiang province contains a further 43m tonnes proven, he said.  

The US Geological Survey (USGS) estimates more conservatively that China’s diatomite reserves are around 110m tonnes, with 430,000 tonnes extracted in 2014. This still puts it second in the world in terms of volume, behind only the US, with reserves of 250m tonnes and a production rate of 800,000 tonnes in 2014.

However, China significantly lags the US in terms of quality. The state of Nevada has a 70% proportion of good quality diatomite compared to 30% of that extracted in Jilin, the province that produces China’s highest quality material, Zheng said.