US1116702A - Process of oxidizing lead. - Google Patents

Description

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alkali metal as a catalytic or facilitating re- ITE if CLIFFORD 1D. HOLLEY, 0F DETROIT, IVIICHIGAN, ASSIGNOIR T0 ACIlWIE 'VTIt-II""lLl ll l'ljl ill-BL ND COLOR WORKSQ O]? DETROIT, ltIIGI-IIGAN, L l, UCJlEtEUItJ-Mtlltlll 01F l llilll.

specification 0t No Drawing".

letters Patent.

Application filed ll'ebrnary ill, will.

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To all whom it may concern.

Be it known that l, CLIFFORD D. Hotter, a citizen of the United States, residing" at Detroit, in the county of ll ayne and State of Michigan, have invented certain new and useful Improvements in Processes of OXldlI/r ing Lead, of which the following is a'speci fication.

This invention relates to processes of oxidizing lead; and it comprises a method of oxidizing metallic lead wherein finely-dividcd lead is oxidized. by air in the presence of a solution containing the nitrate of an agent, such nitrate bein, ordinarily subse quently regained as an alkali, nitrite: such solution being; advantageously a waste liquor derived from the manufacture of lead chrtr mate and containing an alkali nitrate, such as sodium nitrate, as well as, usually, free nitric acid; all as more fully hereinafter set forth and as claimed.

When submerged in or wet with Watr, l'iright surfaces of metallic lead are oxidized by air, if air has access to the liquid, with the production of a. hydrated oxid of lead of basic and reactive properties. With Water alone he reaction never goes very far, neither is it very rapid. even in attrition 'irocesses where the lead oxid formed is kept scoured oil by attrition. With Water containing saline "or other ionizable sub stances, such as acids, and particularly where these acids, as isthe ease with nitric and acetic acids. form solublelead salts, the action is facilitated, partly. probably, at first by remoral of the oiiid from the affected surfaces in the case of the acids and partly, probably. for more obscure reasons connected with the presence of ions. lioth acetic and nitric acids have been proposed for use in such processes. The former is, directly or indirectly, the corroding agent in the Well known Dutch process, which, while yielding a. high gradepinmcnt, is relatively very slow and expensive. The use of nitric acid in proposed 'n-ocesses of making lead oxid has, as a rule, not been successful in practice. in -1n y copending application Serial No. 588,973, filed October 2'5, 1910, l have, however, disclosed a commercially practi :able method of making oxids of lead in which nitric acid is employed. ln the aforesaid application I have also disclosed, but have not claiined specifically, a niodiiied process in which nitrates such as sodium nitrate and the like, either alone or in connection with nitric acid, malt take the place of nitric acid per so. The present application is in part, therefore, a continuation of my prior application aforesaid. ll hcre nitric acid alone is employed it is apt to undergo a far-going reduction, lirst forming lead nitrates and then nitrites with, ulti mately, formation of neutral nitrogen oxide and ammonia. ilcids of course do not lone; remain as such in the presence of the lead undergoing oxidation, but become col'iverted into laid salts by reaction with the lead oxid produced.

1 have discovered that, for some purposes a much better facilitating or catalytic agent is to be found in solutions of the nitrates of the allcalis, such as nitrate of sodium or nitrate of potassium, the former being the better. Nitrates of alkaline earths, such as nitrate of calcium, barium, strontium and magnesium are less suitable and do not yield commercially valuable by-prmluc llnlilre the nitrate of lead, the alkali nitrates do not undergo a far-reaching reduction but arecrmverted into nitrites from which in the course of the operation nitrates are prob ably regei'ierated by the action of the air; these nitrates thus acting); as carrier a cents.

Whatever may be the chemical mccliiihisin of the reactions involved, l have found that a solution of an alkali nitrate. and particu' larly a solution of sodium nitrate, acts an ei'iern'ctic oxidizing agent in the corrosion of lead in the presence of water and air, auichening'tlw operation very imaterially and givii'ig a desirable type of hydra. ba'c and reactive otid of lead from ah white lead, in: ico't, litlnlrgi-l, niiniuni other pitnnentary load product quality may be made. its is well pigmentaly value of oxid ed, leaf :irod: depends very much on their mole." l stitution; it being practically im ossible, for example, to make a ,e'ood red lead, or, in fact, cmnn'iercially, any red lead, from some forms of lead odd, as for example, from. fused litharge. 'ihc hydrated or made under the present inn-anion is re active and molecularly line and. with proper methods of treatment. carries its reactivity and fineness of constitution throughout in.

conversion into other anc pigmentary lead products; giving, for example, a tinegrained dawn, the t till lltl

all

l Oil white lead of good covering power, a fine high grade minium or red lead of unusual volume for its Weight, etc.

After the oxidation of lead in the presence of a solution of an alkali nitrate, the

latter is converted into and remains in such solution as an alkali nitrite; sodium nitrate, for example, becoming sodium nitrite, a commercially valuable product useful for many purposes, as in the dye and color industries. This nitrite may be regained, as by. evaporation of the residual solution from the oxidation and utilized.

A cheap and particularly suitable nitrate solution for the present purposes is found in the waste liquor from the manufacture of lead chromate; a liquid which is ordinarily sent to the sewer and which is hereinafter termed chromate waste liquor. Lead chromate is ordinarily made by double de composition between a solution of lead nitrate and a solution of an alkali bichromate or chromate. Ordinarily sodium bichromate or chreinate is employed; more rarely, the potassium salt is used. Chromate of lead is formedand precipitated by a well-known reaction and nitric acid and alkali nitrate remain in. the solution. With a bichromate, half the nitric acid is free and half is in a combined form. There sodium bichromate and lead nitrate are used as is usually the case, for each molecule of lead chromate formed there remains in the residual solution a molecule of sodium nitrate and a molecule of free nitric acid. This residual solution, or chromate waste liquor, I find particularly suitable for my purposes since it exercises a very vigorous action upon finely divided lead in the presence of airand forms a desirable type of hydrated or basic reactive leadoxid. While solutions for my purpose may be formed by direct solution or" commercial nitrate of soda in Water, I prefer this'chromate waste liquor not only on account of its cheapness but because or" its advantages in practical work.

It seems to be rather more reactive than a directly produced nitrate solution.

The free nitric acid in the waste liquor may be preliminarily neutralized by soda or soda ash to convert it into sodium nitrate; but this is not ordinarily necessary. If not so neutralized however it undergoes farreaching reduction in the process, even so far as ammonia, and is, or may be, ultimately not recovered as a useful product as is the case where it is converted into sodium nitrate which may be recovered later as sodium nitrite. The presence of free nitric acid in the liquor to begin with'is however often advantageousv in my process for the reason that with some varieties or" comminuted lead carrying oxidized coating layers it exercises af solyent action on the oxid in the beginnlngof the operation upon a charge of lead, much accelerating the progress of the oxidizing action.

Any of the ordinary finely divided forms of lead, such as moss lead, dust lead, blue lead and the like, may be employed. Blue fume is not so suitable since it contains lead sulfate and sulfid. Lead shavings and chips are likewise not so well adapted being too coarse. In the present process, the lead should be in a state of quite fine subdivision. Any apparatus adapted to give a good aeration of lead in the presence of liquid may be employed in my process, such as rotating drums and the other apparatus often employed for oxidizing lead by wet processes. lt'is not necessary to use high heats or any heat beyond atmospheric and it is also on: necessary to use artificial cooling.

should be such as to give eiiicient aeration since in the present process the oxygen of the air is relied upon for the major part or" the oxidation, the nitrate acting largely as a facilitating reagent.

Any strength of nitrate solution between two per cent. and 50 per cent. may be em ployed. A solution containing as little as two per cent. is efficient as a catalyzing agent; but with stronger solutions where the sodium nitrite is to be subsequently recovered the operation is cheaper as involving less expense in such recovery. The relative amount of liquid may vary from enough to cover the lead and form a body of iquid to merely enough to convert the lead into a.

the present invention, and where such recovery is efiected of course the use of strong solutions of nitrate producing final strong solutions of nitrite is desirable. While potassium nitrate, or waste chromatc liquor containing potassium nitrate, may be employed in this invention it offers no advantage over sodium nitrate, or waste chromate liquor containing sodium nitrate; and I re gard sodium nitrate, for many reasons, as in any event being rather better adapted for my purposes.

In a practical embodiment of the described prccess, I may place 4000 pounds of dust lead in a drum'with 460 gallons of waste chroma te liquor, containing, say, 8 per-"cent. bfsodium nitrate and 4 per cent. of free nitriacid and agitate with free ac cess of air for 24: to 48 hours. The lead is thereby converted. into a reddish orange hydrated reactive basic oXid of large bull:

for its Weight while the nitric acid of the original solution disappears and the sodium nitrate is converted into an equivalent amount of sodium nitrite. The oxid may be separated from theresidual liquid by any convenient means, such as subsidence and pressing and washing, and may be marketed as it is, or, and usefully, it may be converted into pigmentary products for which its state of subdivision and molecular constitution render it particularly well adapted. By a gentle heating it may be dehydrated and converted into massicot of exceptional quality, while a continuation of the heating under oxidizing conditions converts it into an extremely high grade red lead. By modifying the heating cond|t1ons it may, of course, be converted into a very fine-grained litharge. The hydrated oxid may be gassed with carbon dioxid to convert it into white lead. The chromate 'aste liquor may, or may not, be neutralized with sodium carbonate or bicarbonate preliminarily. If so neutralized the quantity of sodium nitrite to be recovered is increased and some advantages are gained in the operation. The liquor from which the hydrated oxid is separated may be simply evaporated to regain sodium nitrite.

The preliminary separation of the residual liquor may be omittedwhere red lead is to be made, the material being dried and fur naced to produce red lead. The presence of the nitrite facilitates the oxidation to red lead and'after the red lead is formed, the nitrite may then be leached out and regained. In this modification of my invention, in the finishing stages of the first er aerial oxidation the water of the solution may be allowed to evaporate and pass away with the air to a large extent as reducing the cost of the subsequent "drying prior to the red lead oxidation.

Where the nitrite'solution is separated from the hydrated oxid preliminarily to drying and re-oxidation to red lead, if the hydrated oxid be not washed too thoroughly" enough nitrite will remain in it to aid materially in such reoxidation. \Vhile alkali nitrites do not appear to he changed or destroyed to any extent inthe oxidation of lead protoxid to minium or red lead their presence gives a smoother and quicker oxidation with the production of a better article. With small amounts of nitrite, say from one per cent. down, it need not be removed from the finished red lead. A quarter per cent. of nitrite is sufiicient to aid materially in making red lead.

In a typical embodiment of my process in making red lead, finely divided lead may be oxidized by air in the presence of sodium nitrate solution, or Waste chromatc liquor in the manner previously described and after completion of the reaction the lead oxid may be separated from the. bulk of the solution by subsidence and draining and then dried without washing. The drled material may then be furnaced under oxidizing conditions at a low temperature to convert it into red lead and then directly marketed Without leaching.

I claim:

1. The process of oxidizin lead which comprises exposing'finely divi ed lead to the simultaneous action of a solution of an alkali nitrate and of air.

2. The process of oxidizin lead which comprises exposing finely divi ed lead to the simultaneous action of a solution of an alkali nitrate and of air, to obtain a mass comprising oxidized lead and alkali nitrite.

3. The process of oxidizing lead which comprises exposing finely divided lead to the simultaneous action of a solution of sodium nitrate and of air.

4. The process of oxidizing lead which comprises exposing finely divided lead to the simultaneous action of chromate waste liquor containing alkali nitrate and of air.

The process of oxidizing lead which comprises exposing finely divided lead to the simultaneous action of chromate waste liquor containing sodium nitrate and of air, and.

thereafter separating oxidized lead and sodium nitrite.

6. The process of oxidizin lead which comprises exposing finely divi ed lead to the simultaneous action of neutralized chromate waste liquor containing alkali nitrateand of.

air.

7 The process of oxidizin comprises exposing finely divii ed lead to the simultaneous action of neutralized chromate waste liquor containing sodium nitrate'and of air. and thereafter separating sodium nitrite and oxidized lead.

8. The process of making lead oxid which comprises exposing finely divided lead to the simultaneous action .of air and alkali nitrate solution, recovering the lead oxid, and then converting such oxid into red lead by heat and oxidation.

9. The process of making lead oxid which comprises exposing finely divided lead to the .nmltaneous action of air and sodium nitrate solution, recovering the lead oxid, and then converting such oxid into red lead by heat and oxidation.

in testimony whereof, I aiiix my signature in the presence of witnesses.

(ULlFl ORl) l). LHOLLEY.

\Vitncsses:

N. J. Susan, H. E. Crank.