Clean production process of titanium dioxide by sulfuric acid method

Abstract: Titanium dioxide is an important inorganic pigment.

Keywords: sulfuric acid method; titanium dioxide; cleaner production; process research

Abstract: Titanium dioxide is an important inorganic pigment.

0 Preface

When the sulfuric acid method is used to produce titanium dioxide, a large amount of wastes will be generated, which will cause very serious harm to the environment, and it is very unfavorable to improve the environmental protection level of titanium dioxide production

1 Overview of Titanium Dioxide

1.

The chemical composition of titanium dioxide is titanium dioxide, which is a white inorganic pigment with the advantages of non-toxic, opaque, high brightness and high whiteness.

1.

At present, titanium dioxide is mainly used as white paint, applied in coatings, plastics, papermaking, printing and other industries.

The plastics industry is the second largest user of titanium dioxide.

The paper industry is also the main direction of titanium dioxide at present.

2 Production process of titanium dioxide

2.

In the production of titanium dioxide by the sulfuric acid method, sulfuric acid is used to hydrolyze ferro-titanium powder to generate titanium sulfate, which is hydrolyzed to generate metatitanic acid, and then titanic acid is calcined and crushed to obtain titanium dioxide products.

2.

The chlorination method uses titanium-rich slag as a raw material, petroleum coke as a reducing agent, and chlorine gas is added to react at a high temperature to obtain titanium chloride.

2.
3 Method comparison

The two methods have their own advantages, but in terms of environmentally friendly development, the chlorination method is significantly higher than the sulfuric acid method
.
The problem with the current sulfuric acid method is that it is difficult to treat the three wastes.
For example, a large amount of ferrous sulfate, waste sulfuric acid and residues, as well as dilute sulfuric acid and sulfur dioxide gas will be produced during the production process
.
Especially in the production process, a large amount of acidic wastewater and dust will be generated, which will cause serious harm to the environment
.
Relatively speaking, the waste of the chlorination method is relatively small, no dilute sulfuric acid is produced, and the output of waste residue is relatively low, so environmental problems are relatively easy to deal with
.

3 Overview of Cleaner Production

3.
1 Cleaner production concept

Cleaner production is an innovative thinking and method for controlling pollution in the production process.
This method has been widely accepted.
Its goal is to use reasonable environmental protection strategies and technologies throughout the production life cycle to meet sustainable development.
Need
.
Cleaner production requires reducing the energy consumption of raw materials during the production process, removing toxic raw materials, thereby controlling the output of waste generated during the production process, and reducing the toxic substances produced during the production process
.
For the products obtained, the adverse impact on the environment must be reduced throughout the product cycle, and the concept of environmental protection must be fully utilized in the service process to fully meet the needs of environmental protection work
.

3.
2 Implementation Ideas of Cleaner Production

The implementation of cleaner production is systematic, and comprehensive pollution prevention and control measures will be taken for the entire production cycle and the entire product life cycle, such as selecting more scientific raw materials, changing process flow, adjusting process parameters, and optimizing production equipment configuration , Improve operating procedures, etc.
to reduce the generation of pollutants
.
For example, establishing harmless operating parameter selection, improving equipment maintenance methods, and accelerating waste recycling
.

Comprehensive utilization of resources
.
Cleaner production does not mechanically control the pollution in the production process, but will use resources comprehensively, strengthen the transformation of resources, and realize the efficient use of resources in the whole process.
In particular, it will follow the idea of ​​turning waste into treasure and reduce waste in the production process.
And through the comprehensive utilization of the three wastes, the economic benefits of production are improved
.

Improve the production process
.
When improving the production process, by improving the completeness and scientificity of the production process, the production process will be significantly simplified, and the intermittent time in the production process will be reduced, and more production work will be changed to continuous operation
.
Promote technological innovation in engineering by changing process conditions and rational use of raw materials
.

Establish a clean production process in the organization area
.
Cleaner production is established on the basis of ecological principles, relying on the rational arrangement of different production processes to establish a closed loop of materials, all production work will form an organic integrated production system to achieve the effect of comprehensive utilization
.

4 Cleaner production technology of titanium dioxide industry

4.
1 Use high-titanium slag instead of ilmenite

When the sulfuric acid method is used to produce titanium dioxide, ilmenite is used as a raw material, but after the production, there will be management problems such as large acid consumption, a lot of waste acid, and a lot of ferrous sulfate
.
Titanium slag is also an industrial raw material rich in titanium, but its titanium dioxide grade is higher.
For example, titanium slag with a taste of more than 85%, due to its better sulfuric acid solubility, is generally used as a raw material for titanium dioxide chloride
.
Compared with ilmenite, the use of acid-soluble titanium slag as the raw material of titanium dioxide by the sulfuric acid method can obtain higher titanium, and the production capacity of the equipment is also very large, which can use less sulfuric acid and reduce the pressure of environmental protection work
.

From the analysis of process technology, the replacement of ilmenite with high-titanium slag does not add equipment, and after the adjustment of the production process, it can also avoid some processes that consume too much and the operation is too complicated.
For example, it is not needed in the production process.
The concentration and crystallization work can ensure the smooth progress of production, and can also reduce the production capacity of water, electricity, and steam.
Moreover, the whiteness, color reduction power, water-soluble salt and other indicators of titanium production have not changed, so the quality of the product can be improved.
Be assured
.

From an economic analysis, the sulfuric acid consumption of titanium dioxide will also be significantly reduced, and there is no need to use reduced iron powder in the production process, so when using high-titanium slag as a raw material, there will not be too much by-product output, and it will not be obtained.
For other solid ferrous compounds, the use of iron filings is also avoided to affect the quality of titanium dioxide
.

From the environmental point of view, the use of high-titanium slag instead of ilmenite can reduce the discharge of waste water, waste and exhaust gas, especially the gypsum slag produced by waste acid treatment, which has a great positive effect on energy saving and emission reduction
.

4.
2 Supporting sulfuric acid plant

The supporting sulfuric acid plant can directly provide sulfuric acid for the production of titanium dioxide, which can reduce the production cost of raw materials, and can also reduce the steam by-products produced in the sulfuric acid production process.
It can also reduce the amount of steam used in the production process, and the waste heat can also concentrate the titanium dioxide waste.
Acid, but also can reduce the steam used for concentration and reduce the overall energy consumption of the titanium dioxide device
.
For example, using pyrite as a raw material to produce sulfuric acid, although the one-time investment is very high, the price of the raw material in subsequent production is relatively low, and the steam generated can be used in the treatment of superheated steam
.
The slag produced by pyrite can also be sold as a by-product to cement plants, and the ferrous sulfate monohydrate produced by the concentrated titanium dioxide waste acid can also be used as pyrite blending; in order to meet the control of the blending amount, it can also be used Rotary fluidization technology uses dry process to produce ferrous sulfate monohydrate, combined with the sulfur content of pyrite, to determine the proportion of admixture
.
After process update and research, the current maximum blending amount has reached 40%~50%, and blending ferrous sulfate can also convert sulfur into sulfur dioxide and sulfuric acid, increasing the iron content of sulfuric acid burning iron slag
.

4.
3 Air-cooled kiln cooling after calcination

In the process of preparing titanium dioxide, when resource and energy prices continue to rise, comprehensive utilization must be used to solve the waste problem in the production process, especially to deal with high-temperature flue gas to meet the needs of production work
.
In foreign countries, the treatment of high-temperature flue gas generally involves the discharge of waste water after cooling and purification
.
Because the calcination temperature is relatively high, a large amount of cooling water needs to be used when the material is cooled in a water-cooled kiln, and a large amount of water vapor is generated, so that there will be relatively high energy consumption in the production process
.
Due to the large amount of waste heat generated in the calcination stage, the energy can be fully utilized to promote the faster operation of the air-cooled kiln.
This method can save the use of coal on the one hand, and give full play to waste recycling on the other hand.
The role of
.
From the overall cost analysis, the use of this method effectively reduces the overall cost, and the transformation work is completed with only a small investment, so the economic and environmental benefits are very high, and the effect is faster
.

4.
4 Water washing of membrane filter press

Water washing of metatitanic acid is a key production link of sulfuric acid titanium dioxide production.
Through water washing, the insolubility of metatitanic acid can be used to achieve solid-liquid separation of impurities and effectively purify metatitanic acid
.
In actual production, washing will consume a huge amount of water, and the main factors that determine the efficiency of the water system are the filtering equipment and washing equipment, and the effect of washing will also affect the quality of the product
.
At present, the commonly used water washing method is the Mohr filter, but the use of this method covers a large area, and the operation method is very complicated.
There are also problems such as long application cycle and easy pollution during use, and the water consumption during the working process is also extremely large.
, Can not meet the needs of environmental protection work
.
In order to improve the environmental protection level of the washing process, a diaphragm filter press with higher technical content should be introduced to meet the needs of the treatment work
.

The membrane filter press consists of a membrane plate and a chamber filter plate.
During the working process, the slurry will be subjected to the action of the transfer pump to input the slurry into the filter chamber, and the filter cloth in the filter chamber will remove the solids in the slurry.
After filtering out, you can continue to inject air into the diaphragm chamber to squeeze the solids in the filter chamber to achieve the purpose of controlling the moisture content
.
The use of this equipment can change the thrust and direction in the filtering and washing process, meet the requirements of increasing the external force, increase the solid-liquid separation rate in the filtration and ensure the washing speed, reduce the water consumption in the washing process, and can also pass flexible Adjust and control power consumption to make water washing more efficient
.
Moreover, the diaphragm filter press is easier to maintain and has extremely high stability during the working process.
The hydrated titanium dioxide layer will not be directly exposed on the surface of the filter cloth, and it can also avoid the loss of pressure due to accidents and ensure the reliability of production
.
The use of membrane filter presses significantly reduces the utilization of water resources and can also reduce the discharge of wastewater, so it not only reduces water consumption, but also reduces the burden of wastewater treatment, which has extremely high environmental benefits
.
In addition, the diaphragm filter press saves electricity, so there will be very high economic benefits in the production process, which can bring extremely high comprehensive benefits to the enterprise
.

5 concluding remarks

The use of cleaner production technology can improve the environmental benefits in the production process and solve the shortcomings in the past production process
.
When the sulfuric acid method is used to produce titanium dioxide, it is necessary to optimize the original production process from different links, effectively control the titanium dioxide production process, and achieve the purpose of reducing environmental pollution
.

references

[1] Fu Qingyan.
Research on the Cleaner Production Theory and Method of my country's Sulfuric Acid Process Titanium Dioxide Industry [D].
Shanghai: East China University of Science and Technology

[2] Cao Bo, Cui Yan.
Analysis of the clean production process of titanium dioxide by sulfuric acid method [J].
Contemporary Research in Chemical Industry, 2017 (6): 127-128.