When iron ore leaching bismuth trichloride, about 95% of the lead and silver is leached and the leaching solution was cooled filtered, yielding crystalline PbCl 2, wherein the silver concentration is higher, the crystal about 60 to 70% lead, Ag1~4%.
First, the process.
Figure 1.
Figure 1 Process for recovering silver from PbCl2 crystallization
Second, the main technical conditions.
The ammonia leaching was immersed at room temperature, mechanically stirred for 30 minutes, and leached with industrial ammonia water (containing 12 to 15% of NH 3 ), and the liquid-solid ratio was 2:1.
Hydrazine hydrate reduction: normal temperature reaction, mechanical stirring for 30 minutes, hydrazine hydrate (higher than 85%, analytical grade) as reducing agent, water containing strontium amount of 0.8 ~ 1 ml / gram of silver.
Wastewater treatment: using a hydroxide (waste lye, lime milk, etc.), and precipitation for treating wastewater, arsenic and heavy metal ions generated by the second and the insoluble precipitate was separated from the waste. After treatment, the waste liquid contains less than 0.5 mg/L of arsenic; the lead content is less than 1 mg/L, which meets the discharge standard.
Casting: Sponge silver is charged into graphite crucible, and heated to about 1150 °C for melting. The melting time is about 0.6-0.7 hours. Cover the grass ash. After the furnace material is melted, stir it with a wooden rod several times, slag, then cover the grass ash and heat up to Casting from 1200 to 1400 °C. The mold needs to be baked to 120 ° C first, and the calcium carbide smoked mold can produce silver No. 3 with a silver content of not less than 99.9%.
Third, the main equipment.
Two 500-liter enamel tanks (mechanical stirring); one 100-liter ceramic vacuum suction filter; one well-type casting furnace, burning coke ; five sets of vertical casting molds, internal length 370±5 mm, width 135±5 Millimeter, 30 ± 1 mm thick. The mass of silver ingots is 15 to 16 kilograms per piece.
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