The crude bismuth to tin is about 1.5% containing alkali refining production can be sodium stannate. After the crude crucible is melted, first oxidize and remove arsenic . After arsenic removal, the crude crucible is cooled to about 420 °C, and NaOH is added. After the NaOH is melted, NaNO 3 is slowly added during the stirring, and the alkali slag is dried and then removed, and then NaOH and NaNO are added. 3 , repeated several times, the leaf pattern appears on the surface of the sample to be the end point. The solid base and sodium nitrate were added in an amount of: Sn:NaOH:NaNO3 = 1:3:0.5.
The crude slag and slag composition for the production of sodium stannate are listed in the table below.
Table Composition of rough and alkaline tin slag (%)
First, the process
As shown in Figure 1. Production of sodium stannate by tin slag, including leaching, purification, crystallization, drying and the like.
Figure 1 Flow chart of the production of sodium stannate
Second, the main technical conditions
(1) Water quenching. The purpose of water quenching is to separate the beads in the lye and to smash the alkali slag. The water-quenched slag was stirred at 90 ° C until the solution was clear. Heating water quenching can take away half of the arsenic, but also cause some tin loss; it can also be used at room temperature water quenching. Between the end of the control filtrate water quenched density of 1.35 to 1.4 g / cm 3.
(2) Leaching. The purpose of the leaching is to dissolve the sodium stannate in an aqueous solution to facilitate purification. Leaching liquid to solid ratio (3-4) to 1; 4 to 6 hours leaching time, because sodium stannate solubility in water decreases with increasing temperature, sodium antimonate and the solubility in water increases with increasing temperature, it should be used at room temperature Leaching, the leaching rate can be between 85% and 90%.
(3) Purification. The leachate contains Sn 40 ~ 50 g / liter, Pb1 ~ 1.5 g / liter, Sb 0.1 g / liter, should remove lead and bismuth :
In addition to lead: add Na 2 S to remove lead, the temperature is 90 ~ 95 ° C, formulated into a 10% Na 2 S solution, added during stirring, until no black precipitate is produced, the end point, Na 2 S is added in excess.
In addition to sputum: in the concentrated cooking process, adding Na 2 S to remove strontium, can remove most of the strontium in the solution, and then hang the tin to replace the bismuth. At the same time as the lead removal, add the tin plate to the displacement reaction at the boiling point. The solution yellow disappeared, clear and transparent.
(4) Crystal filtration. There are two methods for crystallizing sodium stannate in solution: one is concentrated crystal precipitation; the other is that the solubility of sodium stannate in an alkaline aqueous solution decreases with the increase of NaOH concentration, and stannic acid is added by adding NaOH to the solution. Sodium is precipitated. The former method saves NaOH. The mother liquor is small in volume, but it takes time and steam. The latter method saves time and steam, but consumes NaOH. The mother liquor is bulky, and the two methods are often combined. First, heating and concentration, after reaching a saturated concentration, sodium stannate is gradually precipitated, and dried by centrifugation, which is a commercial sodium stannate.
Third, the main equipment
Alkaline refining uses a 5 ton cast steel pot; centrifugal filter adopts φ600×350 mm, filtration area F=0.66 m 2 ; two concentrating tanks, 1500 liter jacketed enamel reactor and one drying oven.
Fourth, product use
Sodium stannate for the electroplating industry and basic tin-plated copper-tin alloy; textile industry, as flameproofing agents, weighting agents; dye industry as a mordant for further industrial enamel and glass industries.
V. Product quality
Sodium stannate components are (%) Sn37-42, free base (NaOH) 3~5, Pb<0.001, As<0.01, Sb<0.005, Cu<0.03, Fe<0.02, water insolubles below 0.2, nitrate Below 0.2, to tin (Sn 2 + ) meets the test.
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