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