Treatment and recycling of waste acid---for the production of activated clay

Activated clay is widely used, and it can completely replace sulfuric acid to produce activated clay.

First, the significance of using activated acid to produce activated clay

Activated clay is widely used in the decolorization and purification of various mineral oils, vegetable oils, animal oils, paraffin waxes, fatty acids, higher alcohols and benzene. Used as a cohesive contact agent for lubricating oils, as a catalyst for certain petroleum by -products, as a catalyst for gasoline contact decomposition, as an organic synthesis reaction catalyst, as a grease washing and bleaching agent, as a dehydrating, degumming, and as a pharmaceutical external desiccant, or as a botanical antidote, Vitamin A, B adsorbent, desiccant, gasoline gas phase refined preparation, etc. Activated clay is also used to remove toxins (aflatoxins), pigments, malodors, colloidal suspensions, acids, alkalis and moisture in edible oils. It can also be used in soap, plastics, pharmaceuticals, paints and other industries.

Due to the wide use of activated clay, the demand for society is large. The amount of decolorization of petroleum products in refineries is very large. According to statistics in 1992, the annual consumption in the country reached 140,000 tons. Activated clay produced from waste acid can meet the needs of the petroleum decolorization market.

Titanium white powder spent acid plant to produce sulfuric acid may be produced in place of attapulgite clay. A manufacturer with an annual output of 2,000 tons of titanium dioxide can obtain 2,300 tons of sulfuric acid from waste acid. For 440 yuan per ton of sulfuric acid, the annual cost of sulfuric acid can be saved by 1 million yuan, which has good economic and social benefits.

2. Method for producing active clay by using waste acid

1. Preparation of raw materials

1 storage of waste acid. The concentration of the filtrate in the titanium dioxide plant is acid. Some plants have returned all of them to the dilution water and leaching water for acid hydrolysis. The concentrated waste acid and the first water are used to wash the washing liquid with a sulfuric acid concentration of about 6%. Acid storage, as an acid for the activation of intellectual clay.

2 澎 choice of soil. Bentonite can be classified into three types: calcium-based, sodium-based, and hydrogen-based, depending on the type and amount of exchangeable cations containing montmorillonite. Natural hydrogen-based bentonite is rare, and a large amount of calcium-based bentonite is distinguished by the exchange capacity of the exchangeable cations by the basic coefficient K, and K<1 is a calcium-based bentonite, K>1. It is a sodium-based bentonite. Generally, the pH value of the water suspension is 6.4 to 8.5 for the former and 8.5 to 10.6 for the latter, and the base type bentonite must be selected as the raw material of the activated clay.

2. Operation requirements and principles of preparing activated clay

The calcium-based bentonite is dried in a rotary kiln, and the surface water content is required to be 8% to 20%, and then pulverized into a 200-mesh powder, and then activated at a liquid-solid ratio of 2:1. If it is treated with an enamel reaction pot, the waste acid is added first, then stirred and heated by steam. When the temperature reaches 70 ° C, the bentonite powder is added, and then the activation reaction is carried out at a certain temperature, a certain pressure and a certain time. If it is treated with a stainless steel reaction pot with stirring, the stirrer is started after adding waste acid, and heated by the direct fire at the bottom of the pot. When the temperature reaches 70 °C, the bentonite powder is added, and then the activation reaction is carried out at boiling temperature. ~6h, if the reaction evaporates water, add waste acid to supplement it. When sampling and testing the decolorization rate ≥ 90%, the heating can be stopped and discharged.

Bentonite ore has more impurities and less adsorption capacity. After the activation treatment, the bentonite is partially destroyed by the action of sulfuric acid, and the oxides such as aluminum , iron , calcium and magnesium react with sulfuric acid to form a corresponding sulfate, and at the same time, a part of the silicate colloid is formed to make the silica The content is increased to form a porous substance, which increases the specific surface area and improves its adsorption capacity. Bentonite is present in the activation pot together with the sulfate formed by the action of sulfuric acid and the sulfates of titanium, aluminum, iron, magnesium and calcium in the spent acid, which will produce special properties of the activated clay.

The discharged slurry is washed with water by adding a settling agent to wash away the free acid and sulfate substances contained in the surface of the activated clay and the pores, to a free acid ≤ 0.12%, and the pH value is 4.5 to 5.0, that is, vacuum suction filtration The water content is 40%~50%, and the material is discharged in a rotary kiln or a reverberatory furnace at a temperature of 100~200 °C until the water content is <8% (the excessive moisture will affect the decolorization effect). The activated white clay after drying is uneven particles, and the particle diameter is directly related to the contact performance of the produced activated clay. Therefore, it must be pulverized by a high-speed pulverizer or a Raymond machine up to a particle size of 200 mesh to increase it. The specific surface area, which improves the contact performance and the adsorption capacity, is the finished white clay product. [next]

  3, the process

The production process of activated clay is shown in the figure below.

Third, the quality standards of activated clay

The quality requirements for activated clay are shown in the table below.

Quality requirements for activated clay (enterprise standard)

In summary, the following conclusions can be drawn.

1 The waste acid produced by the Titanium Dioxide Factory can completely replace the sulfuric acid to produce activated clay that meets the quality standards.

2 The production of activated clay with waste acid, simple equipment, convenient operation and low investment is a feasible short-flat project.

3 After the activated acid has been activated, most of the acid has been acted upon with bentonite, and the residual acid is returned for use, which will not cause secondary pollution, solve the environmental pollution problem of waste acid, and have good social benefits.