FeCl₃ leache-iron substitution method ^[1]

The method can be divided into three main steps: ferric chloride, hydrochloric acid leaching, iron powder replacement and sponge bismuth smelting

Fig.1 figure for the process flow of FeCl₃ leache-iron substitution method

• Bismuth sulfide was leached with a mixture of ferric chloride and hydrochloric acid. Bi2S3 in the ore was dissolved by FeCl3 to form soluble bismuth trichloride:

At the same time, a small amount of natural bismuth mixed in the ore is dissolved:

The bismuth oxide in the ore was dissolved by hydrochloric acid:

• Iron powder replacement

 The bismuth in the ore is all transferred into the solution after leaching, and the sponge bismuth can be replaced by adding iron powder:

• Bismuth sponge refining

Substitution of sponge bismuth need to be melting to cast into bismuth ingot, but direct melt will cause the happen of severe oxidation reaction. so the melting process in the industry is in the molten sodium hydroxide (melting temperature 318.4 ℃, density 2.13 g/cm3), which not only prevents the oxidation of bismuth, but also facilitates the aggregation of the molten bismuth (melting point 271 0C, isothermal liquid density 10.064g/cm3). In addition the bismuth oxides and certain impurities are asorbed by NaOH.

Advantages of this method

• High extraction rate of bismuth (94% ~ 94.5%)
• Less environmental pollution 

Disadvantages of this method

• High material consumption: Bismuth sponge consumes 1.5 ~ 1.8t hydrochloric acid, 0.4 ~ 0.5t chlorine gas and 0.5 ~ 0.6t iron powder per ton.
• The filtration and washing of slag are difficult

FeCl3 leaching - membrane electrode method2 ^[2]

Properly controlling the potential: the bismuth was reduced at the cathode by replacing the iron powder displacement method with the diaphragm electrode method:

Iron is oxidized at the anode:

• The key of this method is the control of electrode potential and the velocity of solution through the membrane. In case of reducing of electricity efficient due to the ferric ions in the anode area. The anode and cathode were separated by appropriate membrane materials, and the liquid level in the cathode area was higher than that in the anode area.

Advantage of this method

• The process is simple than FeCl₃ leache-iron substitution method

Disadvantages of this method

• Low current efficient (42%-50%)
• The electric oxidation rate of ferric iron is not high

The Methods of Growing Bismuth Crystals

Step 1: Melting the Bismuth ^[3]

• Using the hammer break the bismuth into desired sized chunks
• Place the stainless steel/aluminum cups into the stove top/hotplate and turn it to medium-high
• Wait and watch for the bismuth to begin melting

Fig4. Melting the Bismuth ^[4]

Step 2: Pouring the Bismuth ^[3]

• Set the other stainless steel/aluminum cup into the other stove top/hotplate and turn it on to the same setting as the first one
• Wearing the oven mitts (and tongs if possible), carefully pick up the container of liquid bismuth and quickly pour it into the other cup and set the hot cup aside.
• Turn off the stove top/hotplate that the second cup with the freshly poured liquid bismuth is on.

Fig5. Pouring the Bismuth ^[4]

Step 3: Bismuth Crystal ^[3]

• Wearing oven mitts, gently shake the container again to check and see if the bismuth is becoming solid.
• Quickly pour the liquid bismuth into the first container that was used. There should be bismuth crystals in the second container.
• The bismuth crystals can be snapped out of the container after the bismuth is completely solid, or they whole shape can be saved. Crystals should form in the other container as well.

Fig6. solid the bismuth liquid and take out the crystal ^[4]

References

[1] Chen Y M, Tong X, Lv H Z. Experimental study on recovery of bismuth from copper - bismuth sulfide ore. [J] Multipurpose Utilization of Mineral Resources, 2018

[2] Chen L Xie Z F Huang Q J. Preparation of high purity bismuth sponge from bismuth oxychloride residue. [J] Mineral engineering, 2019

[3] instructables (n.d.). How to make Bismuth Crystals. Retrieved March 24, 2019 from https://www.instructables.com/id/How-to-make-Bismuth-Crystals/

[4] Anne M. H. (2018, September 19). ThoughtCo.. How to Grow Bismuth Crystals. Retrieved March 24, 2019 from https://www.thoughtco.com/how-to-grow-bismuth-crystals-606234