Comprehensive utilization of waste acid

Utilization of waste acid, waste acid hydrolysis mainly refers to the mother liquor by filtration partial titanate i.e., the concentration of H ₂ SO ₄ Total 16% to 22%.

(1) Production of ammonium metavanadate by ammonia neutralization

Ishihara Sangyo Kaisha of Japan using local waste acid and ammonia, so that the pH <4.5, so that the metal sulfate aqueous spent acid iron, aluminum, vanadium, chromium, parsing, iron remained in the liquid phase, separated by filtration After the precipitate, the precipitate is dissolved with waste acid, and then heated to precipitate titanium as hydrated titanium dioxide. The filtrate from which the impurities are removed is reacted with ammonium sulfate, and then cooled to 20 ° C to precipitate ammonium aluminum sulfate (ammonium alum). The reaction formula is as follows :

A1 ₂ (SO ₄ ) ₃ +2(NH ₄ ) ₂ SO ₄ +24H ₂ O→2(NH ₄ ) ₂ SO ₄ ·A1 ₂ (SO ₄ ) ₃ ·24H ₂ O

The mother liquor after separation of ammonium alum is further neutralized with ammonia to form vanadium hydroxide [VO(OH) ₂ ] precipitate, sodium chloride is added to the precipitate, and calcination is carried out in a rotary kiln to form vanadium soluble in water. Sodium (NaVO ₃ ), after cooling, is leached with water and added with ammonium chloride to form ammonium metavanadate precipitate. The precipitate is filtered, washed with water and dried to obtain high-purity ammonium metavanadate (NH ₄ VO ₃ ). The filtrate after the first filtration is added with ammonia and water after separating the vanadium hydroxide, and is oxidized by air to form a precipitate of hydrated iron oxide, and then calcined to obtain iron oxide red (Fe ₂ O ₃ ), and the filtrate is crystallized. six double salt precipitated crystal water magnesium ammonium sulfate _{[MgSO 4 · (NH 4)} 2 SO 4 · 6H 2 O], which is obtained by evaporation of the mother liquor is a high purity ammonium sulfate crystals, which process see diagram 1 .

Although the ammonia neutralization method is very complicated, it can make reasonable use of most of the metal ions in the spent acid, such as titanium: after precipitation of hydrated titanium dioxide, it can be returned to the production of titanium dioxide; iron: after the formation of hydrated iron oxide, Further processing can produce iron oxide red or iron powder, etc.; magnesium: to form ammonium sulfate ammonium double salt, which is a water-soluble fertilizer; vanadium: it can form ammonium metavanadate, can produce iron vanadium alloy and color ceramics , and is also a catalyst; ammonium sulfate: can be used in the return system, can also be used to produce nitrogen fertilizer.

Ishihara Industry Co., Ltd.'s comprehensive utilization technology of waste acid is said to have been industrialized, but China's small and medium-sized titanium dioxide factory is difficult to follow because of its complicated process. [next]

(2) Recovery of cerium oxide from spent acid

Ilmenite contains about 0.0065% to 0.018% by scandium oxide, the spent acid contains scandium oxide 10 ~ 15g / m ^3. A precious metal is scandium, scandium oxide is mainly used in aerospace, military, superconductivity, laser In the industrial sectors such as electronics and electric light sources, many titanium dioxide factories in China have used bismuth peroxide in waste acid. The specific process is not mentioned here.

Scandium present in ilmenite in the form of spent acid hydrolysis of scandium sulfate, mainly obtained by extraction, the extraction agent is typically coal oil, tributyl phosphate, scandium transferred by extraction into the organic phase, and then The white cerium oxide powder is obtained by the steps of alkali stripping, filtration, acid dissolution, precipitation, refining, etc., and the process flow is shown in FIG. 2 .

(3) Production of activated clay

Activated clay, also known as acid white clay, is a decolorizing agent. Its surface is porous and has strong adsorption. It is widely used in the decolorization and deodorization of animal and vegetable oils, fatty acids, soaps, lubricating oils, paraffin, paints and other organic substances. The main raw material for decontamination powder.

The preparation process of activated clay is very simple. The crushed calcium-based bentonite is first dried and dehydrated, then added with waste acid, and heated and pressurized in an activation pot for activation. When sampling and analyzing the decolorization rate of activated clay is >90%, It can be discharged and discharged, and then washed, dried and pulverized to be activated clay.

(4) Production of magnesium fertilizer (iron and magnesium fertilizer) using waste acid

Magnesium fertilizer is: magnesium ferrous sulfate, which is both a magnesium fertilizer and an iron fertilizer. It is widely used in agriculture and is mainly used in saline alkaline soil in northern China. Magnesium sulfate in magnesium ferrous sulfate is a stabilizer of ferrous iron, which can not oxidize ferrous iron into high iron for a long time. At the same time, magnesium in the product can improve fertilizer efficiency, promote plant growth and chlorophyll formation, and is good for preventing yellow leaf disease. Pharmacy.

The production process of ferrous magnesium sulfate is: firstly pulverize the bitter soil (main component MgO≥80%) to a certain fineness (≥200 mesh), and then mix with a certain proportion of compressed air and waste acid (20%~35). %) The reaction takes place as follows:

MgO+H ₂ SO ₄ →MgSO ₄ +H ₂ O

The reaction is an exothermic reaction, the reaction temperature can reach 90-98 ° C, the reaction is complete, then cooled, crystallized, filtered, and the filtrate is concentrated to a relative density of 1.5 to 1.54, allowing it to be naturally cooled to obtain a pale green crystal, and then centrifuged. Dry iron can be obtained. Since the waste acid contains ferrous sulfate, the actual double salt of ferrous magnesium sulfate can be obtained. The mother liquor can be returned to use. The pH can be adjusted again by adding acid, and then industrial magnesium sulfate (MgSO ₄ · can be obtained by concentration and crystallization. 7H ₂ O), the process consumes 2.2t of waste acid per ton of ferro-magnesium fertilizer, 0.2t of rhubarb soil. [next]

(5) Production of iron oxide black using waste acid

The sulfuric acid method titanium dioxide hydrolyzed waste acid contains, in addition to 16% to 22% of H ₂ SO ₄ , about 80 g/L of ferrous sulfate (calculated as anhydrous FeSO ₄ ). By using waste acid to react with scrap iron and iron filings, a ferrous sulfate solution can be obtained. With the ferrous sulfate solution, iron oxide black can be produced according to the method described above, since each ton of iron oxide black consumes about 9 tons of hydrolyzed waste acid. Therefore, the product is also a better way to deal with titanium dioxide waste acid, the process is simple, more in line with China's national conditions. The chemical reaction formula is as follows: See Figure 3 for the process production process.

(6) Production of ammonium sulfate and ammonium ferrous sulfate fertilizer using waste acid and ferrous sulfate

Niobium Chemical Co., Ltd. uses ammonium hydroxide and ferrous sulfate to produce ammonium sulfate. The process flow is shown in Figure 4.

In the above reaction precipitated and Ti (OH) _4, mainly precipitated at pH4 ~ 4.5 A1 (OH) at pH2 ₃ and Fe (OH) _3, pH8 ~ 8.5 when the main precipitate Fe (OH) _2, was added magnetite The main function is easy to filter. The by-product Fe ₃ O ₄ can be used as raw material for steel plant or for producing iron black. Manganese carbonate is mainly used as trace element fertilizer or feed additive.

Chinese Patent No. 97106429,6 also has a method similar to å ºChemistry Co., Ltd., which introduces a method of adding ferrous sulfate to the spent acid, directly introducing liquid ammonia into the mixed solution, and then directly spray-drying the material to obtain Ammonium ferrous sulfate fertilizer.

The use of waste acid can also produce aluminum sulfate, zinc sulfate, elemental powder, potassium sulfate, a desulfurizing agent (a-Fe ₂ O ₃ ·H ₂ O) and the like.