This method is to pH9 ~ 10 mercury-containing industrial waste water was added sodium sulfide, sulfur ions combined with mercurous ion in waste water, the solubility of generated extremely small mercury sulfide precipitation: 2Hg 2 + +S 2 - The mercurous sulfide formed in the reaction is unstable and is easily decomposed into mercury sulfide and mercury. The solubility of mercury sulphide is 1.4×10 -24 g ∕L. Because the amount of mercury contained in the wastewater is small, the mercury sulphide formed is mostly fine particles, and most of the suspended mercury is not easily precipitated in water. For this purpose, the coprecipitation agent and the fractional precipitation method are often used. I.e., first input slight excess of sodium sulfide, mercury and mercury sulfide is then put into an appropriate amount of ferrous sulfate, so that excess liquid sulfur iron sulfide precipitate. At this time, a part of the ferrous iron may also form a Fe(OH) 2 precipitate with the hydroxide ions in the water. Since the solubility product constants of mercury sulfide and iron sulfide in water at 18 ° C are 4 × 10 -53 and 6 × 10 -18 , respectively, the difference between them is hundreds of millions of times. After the addition of FeSO 4 , the sulfur in the solution must first form Hg 2 S with mercury before the FeS precipitate is formed. Therefore, the input of ferrous sulfate not only can quickly remove excess sulfur ions in the wastewater, but more importantly, as a coprecipitation carrier, the Hg 2 S of the particles can be adsorbed on the surface of the floc of FeS to form a complete precipitate. The purpose of precipitating mercury. In a chemical plant in China, the process and conditions for treating 5 mg ∕L of acidic wastewater from acetaldehyde workshop by sodium sulfide co-precipitation method are as follows: First, mixed neutralization The acidic wastewater is pumped to the mixer, and at the same time, the lime milk (or calcium carbide slurry) in the stirring tank is pumped into the mixer, and when the wastewater has reached half of the batch throughput, the supply of the lime milk (or calcium carbide slurry) is stopped. . The mixture is placed in a wastewater treatment tank and the other half of the wastewater is pumped into the tank. The mixed wastewater in the wastewater treatment tank is thoroughly mixed and stirred under the stirring of the stirring blade, and when the pH value is determined to be 9, the neutralization operation is completed. Second, co-precipitation First, add 3% sodium sulfide solution to the wastewater, stir for about 10 minutes, add 6% ferrous sulfate solution, stir for about 15 minutes, let stand for half an hour, and take the supernatant to analyze the mercury content to meet the requirements. Dehydrated by a centrifuge. The separated mercury slag is concentrated. The supernatant is diluted with water and discharged. The acidic wastewater containing 5 mg/L of mercury was treated by the above procedure, and the dosage was: sodium sulfide 30 mg ∕L, ferrous sulfate 60 mg ∕L. When the pH of the neutralized solution is in the range of 8 to 10, the method can completely remove the inorganic mercury in the wastewater. In addition to the sodium sulfide co-precipitation method, the treatment of mercury-containing wastewater by sodium sulfide co-precipitation flotation has also been successful in Japan. This method is divided into three methods of adding trivalent iron salt flotation, adding sodium sulfide flotation and adding sodium sulfide and adding trivalent iron salt flotation. When the pH of the waste liquid is about 9, Fe 3 + is added, and three-stage flotation is carried out with sodium oleate; or according to the total content of mercury in the waste water, it is effective to add a stoichiometric amount of sodium sulfide flotation twice. When the waste liquid has a pH of 6.5 to 9.5, it is effective to add Fe 3 + 40 mg of ∕L and sodium sulfide having the same total amount of mercury, even if only one stage of flotation is carried out with sodium oleate. The waste water purified by this method was found to have no mercury. Commercial Heat Pump Water Heater Electric Water Heat Pump,Electric Heat Pump Hot Water Heater,9kw Heat Pump,12kw Heat Pump Guangdong Y.K.R New Energy Co.,Ltd , https://www.ykrnheatpump.com
Hg 2 S↓ HgS↓+Hg