The process of preparing photovoltaic glass from high-purity quartz sand

Photovoltaic glass, as the core material of crystalline silicon solar cell module, has strict requirements on light transmittance and impurity content, in which the purity of quartz sand directly determines the performance of the glass. This paper is based on the research results of ‘New Technology for Preparation of High Purity Quartz Sand for Photovoltaic Glass’, systematically combing the preparation process and key technology of high purity quartz sand. 

I. Raw material selection and pre-treatment 

1. Raw Material Selection 

The preparation of high-purity quartz sand requires low-iron quartz ore as raw material (Fe₂O₃ content should be less than 0.014%). High-quality quartz sand that can be directly utilised in nature is scarce, so common quartz ores need to be processed through beneficiation and purification techniques. 

2. Washing and Classification Desliming 

- Purpose: Remove soil, clay minerals and some mechanical impurities from the surface of quartz sand. 

- Process: After the raw ore is washed, the fine-grained impurities are separated by the classification and desliming equipment (such as spiral classifier). 

- Effect: It can significantly reduce the content of aluminium and iron impurities, but the effect on surface film iron and clay minerals is limited. 

II. Physical purification process 

1. Mechanical Scrubbing 

- Principle: use mechanical force and friction between sand particles to remove surface film iron and adhesive minerals. 

- Equipment: bar scrubber or organic scrubber, slurry concentration control at 50%-60%. 

- Key Parameters: Scrubbing time needs to be balanced between removal effect and energy consumption to avoid excessive wear and tear on the equipment. 

2. Magnetic Separation

- Role: Remove weak magnetic impurities (such as hematite, limonite, black mica). 

- Equipment: Wet strong magnetic separator or high gradient magnetic separator. 

- Optimisation: The finer the particle size of quartz sand, the higher the efficiency of magnetic separation; multiple magnetic separation can gradually reduce the iron content.  

3. Flotation: Objective: Separate the non-ferrous metals from the quartz sand. 

- Objective: Separate non-magnetic impurities (e.g. feldspar, mica). 

- Process: Adopt non-fluorine flotation method (sulfuric acid adjust pulp pH=2, with aliphatic amine salt collector), avoid fluorine wastewater pollution. 

- Effect: The purity of quartz sand can be increased to 99.3%-99.9%.

4. Colour Separation

- Technology: Based on the difference of optical properties, foreign colour particles (e.g. titanium and chromium impurities) are eliminated by colour sorter. 

- Application: It is especially suitable for removing minerals with small colour differences, and improving the appearance and light transmission of the final product. 

III. Chemical purification process

1. Acid leaching and pickling

- Acid leaching: Static immersion method using sulphuric acid, hydrochloric acid or mixed acids to dissolve metal impurities (Fe, Al). Hydrofluoric acid (HF) should be used with caution (concentration ≤10%) due to the dissolution of quartz. 

- Acid washing: Dynamic continuous process, using fluidised bed technology to achieve reverse contact between raw sand and acid, highly efficient iron removal. 

  - Advantage: Waste acid can be recycled, acid mist is recycled and treated, high environmental protection. 

  - Case: An enterprise in Anhui adopts the integrated fluidised bed pickling system, with an annual capacity of 600,000 tonnes, and the Fe₂O₃ content of fine sand ≤0.007%.

2. Microbial leaching

- Principle: use microbial metabolites such as Aspergillus niger to dissolve thin film iron on quartz surface. 

- Effectiveness: Removal rate of Fe₂O₃ exceeds 75% in laboratory stage, and iron content of fine sand is as low as 0.007%. 

- Challenge: Industrial application needs to solve the problem of strain culture stability and scale production efficiency. 

IV. Process Combination and Optimisation 

1. Multi-Technology Combination

A single method is difficult to meet the purity requirements, need to combine physical and chemical processes. Typical processes are: 

Water washing→scrubbing→magnetic separation→flotation→acid washing→colour separation. 

2. Parameter control

- Particle size management: The particle size of quartz sand needs to be concentrated at 0.113-0.55mm (≥94.5%) to avoid too coarse or too fine affecting the melting efficiency. 

- Environmental protection measures: Waste acid neutralisation and purification, tail gas recycling, waste water recycling to achieve green production. 

V. Technological Challenges and Development Direction 

1. Resource bottleneck: Global high-purity quartz sand relies on a few countries (such as the U.S. Unimin), China needs to break through the purification technology to reduce import dependence. 

2. Cost control: the industrialisation of microbial leaching and continuous pickling needs to further reduce energy consumption and reagent consumption. 

3. Intelligent upgrading: develop automated mineral processing equipment and AI process optimisation system to improve production stability. 

Concluding Remarks 

The preparation of high-purity quartz sand is the core link of the PV glass industry chain, which can promote the upgrading of China's photovoltaic industry in the direction of high value-addedness through physical-chemical coupling technology, environmental protection process innovation and efficient use of resources. In the future, it is necessary to strengthen technical research and development and cross-border cooperation, break through international technical barriers, and help achieve the goal of ‘double carbon’.