Iron precipitate from filters, dissolving

Table II. Dissolving Iron Precipitate from Filters...

OxideofOoba.lt, the ores of which, after grinding and roasting, to drive off as much as possible the excess of arsenic and sulphur, are dissolved in hydrochloric add, sometimes with the addition of a small quantity of nitric acid. The copper, lead, silver, arsenic, antimony, el cetera, are precipitated by sulphide of hydrogen, and to the filtered solution carbonate of lime is added in (he form of chalk, by which all the iron, alumina, and a trace ot cobalt are thrown down, the nickel and cobalt remaining in solution. To this solution which must ho hot and neutral, a solutien of bleaching powder is added in sufficient quantity to precipitate the cobalt, and the menstruum is then well boiled to remove the chlorine as fast as possible. The oxide of nickel is afterwards precipitated from the filtrate by the addition of hydrate of lime, and ebullition. 

Extraction.2 — (a) To extract gallium from an ore, the material is ground to a fine powder, dissolved in aqua regia, and the excess acid expelled by heating. Cool, add zinc, and filter off the precipitated metals, then boil for a long time with zinc, when a basic gallium salt is precipitated along with aluminium, iron, zinc, etc. 

Sj. When the ore or alloy contains tin, dissolve in HCl + Fe Clg, distil off As, precipitate Sb with metallic iron, redissolve, after washing in HCl plus a little KCIO3, filter off the insoluble impurities derived from the iron, precipitate Sb with H S, and proceed as under yj. 

Thus, Figure 4.4 shows a pressure vessel filter, operating in upflow mode, and developed for the removal of dissolved iron from water supplies. The filter medium takes the form of a bed of catalysed manganese dioxide in grannlar form, approximately 1 m deep. This medium has the ability to cause dissolved iron to react with the oxygen present in the water to form insoluble iron oxides, which will precipitate and be retained by the bed. Cleaning is then undertaken by a high velocity backwash process which fluidizes the bed medium and removes the precipitated iron. 

In a copper or iron kettle of 4-I. capacity is placed a solution of 200 g. of d-tartaric acid and 700 g. of sodium hydroxide in 1400 cc. of water. A 12-I. flask through which cold water is run is placed in the mouth of the kettle in order to prevent loss of water vapor, and the mixture is boiled gently over an open flame for four hours. The solution is now transferred to a 12-I. flask or crock and partially neutralized with 1400 cc. of commercial hydrochloric acid (density 1.19). To the still alkaline solution is now added just enough sodium sulfide to precipitate all the iron or copper which has been dissolved from the kettle (Note i). The filtered solution is then just acidified with hydrochloric acid, boiled to expel all hydrogen sulfide, and made very faintly alkaline to phenolphthalein with sodium hydroxide solution. To the hot solution is then added a concentrated solution of 300 g. of anhydrous calcium chloride which causes an immediate precipitation of calcium tff-tartrate and mesotartrate. 

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