Reprocessing The Waste Liquid That Contains Fluorine, Generated By Manufacturers Of TFT-LCD Panels.

In the display panel production process, a thinning process is used to obtain a thinner display panel by etching the glass with hydrofluoric acid, resulting in the generation of high fluorine waste acid. Table 1 shows the components of the high fluorine waste acid.

High fluorine waste acid can be used to produce industrial products such as hydrogen fluoride (AHF), boron trifluoride (BF3), hydrochloric acid (HCl), and sulfuric acid (H2SO4).

Flow Chart:

The high fluorine waste acid, generated during the thinning process in display panel production, can be used to produce industrial products such as anhydrous hydrogen fluoride (AHF), boron trifluoride (BF3), hydrochloric acid (HCl) and sulfuric acid (H2SO4).

To produce these products, high fluorine waste acid is mixed with concentrated sulfuric acid, and fluorosilicic acid is decomposed into hydrogen fluoride (HF) gas and silicon tetrafluoride (SiF4) gas at appropriate temperature and pressure. When the panel glass contains boron, fluoroboric acid and fluoroborate decompose to produce boron trifluoride (BF3) gas.

The HF, SiF4 and BF3 gases are then volatilized in the presence of concentrated sulfuric acid. The HF gas is condensed into HF liquid and rectified to obtain AHF. Alternatively, it can be absorbed with pure water to obtain 49-55% pure hydrofluoric acid, which is then returned to the thinning production line for reuse.

The remaining gas enters the BF3 gas absorption tower, where BF3 gas is absorbed by solvent and becomes liquid. Boron trifluoride gas can be obtained after desorption and refining, or absorbed into fluoroboric acid by water for harmless treatment in the sewage treatment station.

The non-condensable gas SiF4 enters the absorption tower, and after three-stage absorption by pure water, it becomes highly concentrated fluorosilicic acid, producing silica precipitation. Wet silica product is obtained by separating silica and cleaning, and it can be sold to glass factories as raw materials. High-fluorine silicic acid is returned to the high-fluorine waste acid solution for recycling and decomposition.

The by-product of wet silica products is packaged, warehoused, and naturally dried. It can be sold to glass factories as raw materials, and the mix of unsellable silica and water is pumped to the sewage treatment station for harmless disposal.

After the regeneration and recovery process, the HF recovery rate in the high fluorine waste acid is about 93 ~ 97%.

The concentrated sulfuric acid obtained from the previous process is separated into dilute sulfuric acid and sulfate using a diffusion dialysis membrane to obtain pure dilute sulfuric acid.

The sulfate is treated at a sewage treatment station. The dilute sulfuric acid is heated and concentrated at high temperature to obtain concentrated sulfuric acid with H2SO4≥92%.

Part of the concentrated sulfuric acid is recycled in this device, and the surplus can be used as raw materials for the thinning production line or sold as products.

The water vapor produced during sulfuric acid concentration is condensed into wastewater with H2SO4≤1.0% and HF≤0.1%, which is then treated at a sewage treatment station.