Chlorination refining example

After removing the silver , the sputum is pumped into the No. 4 pot for chlorination refining. Cool down to 320 ~ 340 ° C into the chlorine gas, each pot into the 4 to 8 chlorine tube, the insertion depth of 300 ~ 400 mm. Cannula too shallow, the chlorine gas escapes easily volatile, lower liquid containing high lead chloride is difficult, the cannula is too deep, the resistance through the large chlorine, chlorine steel pan susceptible to corrosion.

Zinc chloride, m.p. 283 deg.] C, due to the low density (2.9 g / cm 3), float to the liquid surface while covering effect, off-white pan surface forming a thin film, when the slag began to appear dark gray, in addition to zinc was end, at which time The liquid zinc chloride slag is taken out as a raw material for producing ZnCl 2 .

Then chlorination removes lead. Since lead is the main impurity in the mash, in order to speed up the chlorination and lead removal and increase the chlorine utilization rate, the operating temperature is generally controlled at 350 to 400 °C. PhCl 2 has a density of 5.9 g/cm 3 and a melting point of 498 ° C. It is lighter and floats than the sputum, and the solid scum covers the surface of the sputum to prevent the loss of chlorine gas and environmental pollution. Process to remove lead chloride, lead slag fish several times, when the first stop chloro slag, heated to above 500 ℃, liquid was scooped out so as to reduce the slag entrained in the metal bismuth losses. It is not necessary to remove the slag from the middle of the journey. After each fishing, it will still cool down to 350-400 ° C, and continue to pass chlorine until the end of lead removal. The amount of zinc chloride slag is about 3% to 5% of the weight of the material, and the amount of lead chloride slag is about 13% to 20% of the weight of the material. The composition thereof is shown in the following table.

Table Chlorination refining slag composition (%)

The judgment of the end point of chlorination and lead removal is extremely important. Judging too early, because the lead removal is not complete, the lead removal process is added before the pot is removed. If it is judged too late, the amount of slag lost due to chlorination will increase. The end point of the judgment can be based on the lead content of the lead in the rough, and the lead output of the lead is roughly estimated. In the production practice, it is mainly judged by taking the sample visually: when the surface of the sample is black, no metal beads are taken, and the test section penetrates the dense vertical stripe crystal, which is metallic luster, and there is no gray spot, which is the lead end point. At this time, the sputum contains lead less than 0.01%, and then continues to pass chlorine for about one hour. The lead is sampled and analyzed, and the lead content fluctuates between 0.0005% and 0.001%.

Chlorine gas is highly toxic, strongly irritating the human respiratory system. Inhalation of excessive chlorine can cause pulmonary edema and even death.

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