Introduction of mercury-containing wastewater treatment process
A, mercury-containing waste water Pollution
In the production of gold, still using the job of gold amalgamation process. In the production process, a lot of mercury is lost to the wastewater. Mercury plate effluent, flotation tail water, thickener overflow water, gold concentrate section drainage, these turbid water contain mercury.
According to the water quality monitoring results in the “Investigation on Mercury Pollution in Gold Mines†by the Changchun Gold Research Institute of the Ministry of Metallurgical Industry in 1987, the turbid water discharged from the tailings dam exceeded the comprehensive wastewater discharge standard (GB8978-88), and the total over-standard rate reached 27.5%. Exceeding the national surface water standard, the over-standard rate is 100%. Most of the drainage outside the tailings dam of each mine is turbid water, which poses pollution to the environment and brings certain harm to the health of the population. Therefore, it is necessary to manage the rear side.
Second, mercury-containing wastewater treatment methods
There are many treatment methods for mercury-containing wastewater. The effectiveness and cost of the various treatment methods depend on the presence of mercury, the initial concentration, the coexisting ions in the wastewater, and the criteria for achieving the effluent quality.
(a) reduction method
1 / NaBH 4 (sodium perborate) chemical reduction method Principle: non-metallic reducing agent - sodium borate, and after the reaction is mainly generated mercury and mercury metaboric acid, hydrogen.
Hg 2 + +BH 4 - +2OH - <=>Hg↓+3H 2 ↑+BO 2 -
The redox half-reaction is:
Hg 2 + +2e=Hg
B 5 - =B 3 + +8e
6H + +6e=3H 2
Reaction conditions: pH=11
The generated mercury particles (having a particle size of about 10 μm) were separated by a hydrocyclone to recover mercury remaining in the superfluous water, and after separation by water vapor, it was trapped with a filter having a pore size of 5 μm. 2 kg of mercury can be recovered per kg of NaBH4.
2. Metal reduction method Where the oxidation-reduction potential is lower than Hg 2 + , such as Cu.Zn.Fe.Mn.Mg..Al, etc., the corresponding metal chips can be packed into a packed tower to replace Hg2+ ions in the wastewater. Take iron as an example: Fe+Hg 2 + =Fe 2 + +Hg↓
The replacement rate is related to factors such as pH, temperature, metal purity, and contact area.
Organic mercury cannot be directly reduced or replaced with a metal, and is usually destroyed by an oxidizing agent (such as chlorine); it is converted into inorganic mercury and then replaced with a metal.
(2) Vulcanization method
Chemical principle: H 2 + +S2-=HgS↓
2Hg 2 + +S-=Hg 2 S<=>HgS↓+Hg↓
The sulfide product produced by the reaction has a small solubility product, such as KsP of HgS = 4 × 10 -1 , and KsP of Hg 2 S = 1.0 ÷ 10-45.
It can be seen that the sulfide precipitation method is a high-efficiency mercury removal method.
If there is an excess of S 2- ions in the wastewater, ferrous sulfate (FeSO 4 ) may be added to form an iron sulfide precipitate with an excess of S 2- ions. FeSO 4 +S 2- 2- FeS↓+SO 4 2- Add a part of Fe 2+ , which can combine with OH- ions in wastewater to form Fe(OH) 2 and Fe(OH) 3 , for a small amount of tiny HgS aerosols, Co-precipitation and coagulation sedimentation. The addition of FeSO 4 does not affect the preferential precipitation of HgS. Because the solubility product of the generated FeS (KsP = 3.7 × 10 -19 ) is hundreds of millions of times larger than the solubility product of HgS.
In actual production, the pH is adjusted to 8 to 9 with lime, the wastewater is alkaline, and FeSO 4 is added . Removal of mercury by sodium sulfide precipitation method can reduce the amount of mercury in wastewater to 1~0.1mg/L, and can take iron filings, activated carbon adsorption, coagulant precipitation, etc., so that the mercury content in wastewater is reduced to 0.05~0.01mg/L. the following.
(3) Adsorption method
Activated carbon is often used as an adsorbent in China.
The specific method is to use static adsorption method, first precipitation, and then adsorption.
First, sodium sulfide is used to convert mercury ions into mercury sulfide precipitates, and at the same time, suspended solids such as silt in wastewater are removed, pH is adjusted with calcium hydroxide, and ferrous sulfate (FeSO 4 ) is used as a coagulant to adsorb the leaked metallic mercury with activated carbon. And mercury compounds, such treated liquids contain residual mercury that meets national emission standards.
Foreign agricultural and sideline products containing tannin are used as adsorbents in foreign countries. Such as: walnut slices, peanut soft skin, straw, peanut shell, bagasse, olive core and so on. Some are treated with clay and used as adsorbents. Such adsorbents containing tannins are treated, and when mercury-containing wastewater contains other metals at the same time, the adsorption effect on mercury is not affected. And its adsorption capacity exceeds 130% of activated carbon.
(4) Ion exchange method
Several resin columns are packed into a wastewater purification series, so that mercury-containing wastewater passes through several exchange columns, and mercury is not detected in the effluent.
(5) Condensation precipitation method
The coagulant uses lime.
Adding lime to the mercury-containing wastewater to form Ca(OH) 2 and Ca(OH) 2 has a cohesive adsorption effect on mercury, and the effect is better in the presence of trivalent iron ions. The use of aluminum sulfate as a coagulant to treat mercury-containing wastewater has a good effect. After coagulation and sedimentation, the mercury content of the effluent water can be reduced to less than 0.05 mg/L.
(6) Solvent extraction method and other methods
At present, foreign countries have used triisooctylamine-xylene to extract mercury-containing wastewater. After extraction, the residual mercury in the purification solution is below 0.017t, g/L.
The extractant after mercury extraction is back extracted with a non-acid salt to recover mercury.
In addition, foreign countries use microbial recovery of mercury, electrolytic recovery of mercury, ferrite precipitation method for mercury removal, sulfide precipitation-flotation separation method for mercury removal, and domestic research on conversion mercury removal, humic acid-containing coal adsorption method for mercury removal. Wait.
At present, mercury is extracted from the ammonia operation, and the mercury lost to the water is discharged to the tailings pond. It stays in the tailings pond for a period of time. Under the action of gravity, it is naturally settled and discharged from the tailings pond into the surface water. Can reach the ground water quality standards.
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