Influencing factors and operational precautions of Nitric ac
2020-07-28 10:00Introduction：Influencing factors and operational precautions of Nitric acid dissolution silve r method in t he proces s of gold mud smelting Containers for gold and silver separation are generally made of stainless steel drums or enamel reactors. In or
Influencing factors and operational precautions of Nitric acid dissolution silver method in the process of gold mud smelting
Containers for gold and silver separation are generally made of stainless steel drums or enamel reactors. In order to facilitate agitation and avoid a large number of bubbles produced in the reaction resulting in a solution overflow, the amount of raw material added should not exceed 20% of the volume of the container.In the initial stage of silver separation, the reaction is very intense after adding nitric acid. Therefore, the amount of acid added must be controlled very carefully, and it cannot be heated or stirred in the process of adding acid, so as to prevent the reactant from overflowing the container. At the same time, the production site should prepare enough cold water to cool and dilute if the reaction is too intense. After the reaction is stable, the reaction is heated and stirred, and add acid and water according to the specific conditions, and the ratio of liquid to solid is adjusted to 3: 1.
carrying gold steel wool can be dissolved by 10% ~15% nitric acid (prepared with hot water), and then treated with electric MPF mud.It can also be mixed with a certain amount of nitrite, quartz, and borax and smelted after drying, and then throwed beads and seperated sliver
The addition of nitric acid is an important step in the separation of gold and silver. Nitric acid should be added in stages according to the reaction conditions. Before adding acid in each stage, the products of the previous stage should be washed with hot water for two or three times to reduce the ion concentration of the dissolved substance in the solution and to expose the fresh surface of silver and other base metals to the full. To facilitate the next phase of the reaction to be fully carried out.
The concentration of acid increased from dilute to dense with the reaction. In the initial stage of the reaction, dilute acid with nitric acid: water of 1:( 4~8 )was added, because the content of silver and other base metals was large at this time, the reaction was easy to carry out, and the addition of dilute acid could save the amount of nitric acid, as can be seen from the reaction formula. The acid consumption of dilute nitric acid is 1/3 less than that of concentrated nitric acid. In addition, for gold slime formed by gold-carrying steel wool, due to the presence of a large amount of iron, the formation of trivalent iron ions can be avoided by adding rare nitric acid, and the iron can be sufficiently leached.
As the reaction proceeded, the content of silver and other base metals in the gold slime gradually decreased. Near the end of the reaction, the gold content had reached more than 90%. At this time, only a higher concentration of nitric acid was added and increased the intensity of stirring in order to make the remaining silver and other base metals fully dissolved.
It has been proved that heating the reaction is the key to complete silver separation in the process of silver separation with nitric acid. Generally, the reaction temperature should be controlled at about 90℃. The temperature is too low, the reaction speed is too slow, the temperature is too high, the reaction is violent, should not be controlled. When the temperature is over 350℃ and the concentration of nitric acid is more than 70%, the gold will be corroded, and the decomposition rate of nitric acid will be accelerated and its utilization ratio will be reduced.
If a stainless steel drum (basin) is used as a reaction vessel and is heated by an electric furnace, special attention should be paid to strengthening the stirring at the end of the reaction, because the acid concentration is high, the reaction is slow, the bottom of the container is dense and the gold mud deposits are dense, and the local temperature is high. Insufficient contact with acid, gold mud easily caking at the bottom and melting on the bottom of the barrel (basin).
The separation of gold and silver by nitric acid generally needs 3 ~ 4 batches of leaching, 3 ~ 5 h per batch. According to the color of gold mud can master the reaction end point, generally gold mud red and yellow can be seen. It can also be determined according to the reaction condition that under the heating condition (above 80 ℃), the liquid surface does not turn over obviously and the yellow smoke is no longer produced and the end point is reached after the nitric acid is added 5min. For the inexperienced, it is best to determine the end point based on the concentration of silver ions in the leachate.
After the reaction was finished, the deposited gold mud was washed and filtered with hot water, and the white precipitate was not found in the salt water, and the final washing solution was neutral. After washing, the gold mud can be melted after drying.
After purification by silver nitrate , the amount of gold is generally over 90 % , the total amount of flux added in smelting is one - third of the total amount of gold mud ,and adjust the ratio of borax, sodium carbonate and nitrite according to the specific situation, The silicic acid content of slag controlled is between 1.4 and 1.6. In this case , the melting point of slag is 1100 ℃, and the fluidity of slag is good. During the smelting process, all the gold slime should be kept in heat preservation for 0.5 h after melting, so that the gold and impurity can be separated fully, and then the ingot can be cast. The surface of the cast gold ingot is smooth and complete. There are no obvious metal particles in the slag,and the gold content in the slag is below 90g/t.
