US2323982A - Manufacture of white lead - Google Patents

Description

Patented July 13, 1943 MANUFACTURE OF WHITE LEAD Edward J. Dunn, Jr., Manhasset, N. Y., assignor to National Lead Company, New York, N. Y., a

corporation of New Jersey No Drawing. Application October 31, 1939, Serial No. 302,137

2 Claims.

This invention relates to a process for manufacturing basic lead carbonate or white lead of special and highly improvedpigmentary properties.

More particularly, the invention relates to the accelerated corrosion of an economical type of litharge-metallic lead mixture in the presence of carbon dioxide, water and dilute acids, e. g., acetic acid, to a superior product for use as a paint pigment, and is based on my discovery that a finely divided litharge containing amounts of finely divided metallic lead will be corroded in a single step in a much shorter time than heretofore possible.

One of the improved features of my novel process lies in the fact that there is obtained thereby an increased yield of finished product over that obtainable by the usual prior art processes. Furthermore, the product itself is superior to that produced by prior art processes.

I am aware that a number of other means have been proposed by the prior art for corroding litharge or finely divided lead with carbon dioxide in the presence of water and acids. All such corrosion processes, however, require two steps to produce good quality White lead. My process, on the other hand, produces in one step a. superior pigment in about three days, thereby effecting a considerable saving of time.

I am also aware that there have been suggested so called quick processes in which a liquid phase of a lead salt in solution is reacted upon to producea basic leadcarbonate. Such processes are known" "as'precipitation processes and are readily distinguishable from my present invention which embraces a corrosion or socalled dry process. Where, therefore, reference is hereinafter made to prior art processes, it will be understood that dry processes are meant.

Broadly, in the exercise of my present invention, mixtures of lead oxide and metallic lead, in--which the finely divided metallic portion is beiween and 55 percent of the total, are charged into rotary cylinders of the type described in United States Patent No. 1,447,740. Of course, it is evident that, if desired, a battery of short cylinders rather than the long cylinder for continuous operation described in the aforesaid patent may be employed. woxide gas is then introduced into the eyligders to react on the leadoxide-metallic leadcharge, which is kept in a damp condition by periodic sprinklings with ater an d acid, e. g., acetic acid. In about three aays'timme initial charge will be corsentially of c ,-Water and acidw ilie charge is kept in a dapened condi tion by sprinkling with water or dilute acid. In

about four to six days corrosion diminishes so that the batch has to be removed and disintegrated, to allow new surfaces of metal to be further corroded. If this is not done, a very poor quality white lead would result, which could not be marketed. This disintegrated product of the first step is then again charged into the rotary cylinders so that the corrosion may continue until the metal content is fairly low. This second step usually takes six days or more. My process involving the use of a starting material, viz., a lead oxide-metallic lead mixture, difiers from any previously employed by the prior art, completely eliminates the first step and its consequent disintegration, and accomplishes what usually takes place in the second step in just about half the time.

In the usual two-step corrosion process, a low quantity of carbon dioxide must prevail to insure against over-carbonation and prevent coarse particle formation with consequent poor pigment qualities. My invention can Successfully use large quantities of carbon dioxide without over carbonation and still give a high yield and a pigment which has high paint-thickening and covering powers.

In the usual two step corrosion process carried out as hereinabove described, acid is introduced upon the charge partly in the first step and partly in the second. In my process, as a consequence of my single step improvement, all the acid, preferably acetic acid, may be put on in the twenty-four hours following an initial four hour run. Moreover, in the usual prior art processes, the quantity of liquid sprinkled on to the charge, of necessity, has to be diminished as corrosion progresses, thereby slowing up the reaction in order to avoid "killing" or stopping the corrosion and producing coarse pigment particles which would have low covering power. In

Example About 6,000 lbs. of finely divided litharge containing about 40 percent of finely divided metallic lead were charged into a cylinder of .the usual type, rotating slowly at about nine revolutions per hour while was containing between eleven and thirteen percent of carbon dioxide was introduced into the cylinder at the rate of about thirty-five cubic feet per minute. The charge was then wet down with water by automatically sprinkling once at each revolution for an initial period'of four hours. At this stage of the process, the charge, being warmed by the reaction taking place, was constantly steaming. Then acetic acid solution of a strength of about six percent, was cut into the sprinkling system for a period of twenty-four hours, in the ratio of about 1% quarts for each sprinkle 0r revolution. All the acid to be used was thus put on the charge. Corrosion continued for forty-eight hours more during which time the sprinkling, now with water alone, was raised to approximately 1% quarts per sprinkle or revolution. During the last six hours of corrosion the cylinder was sprinkled by hand as well as by matic sprinklers so as to soften the batch before "dis charge? the stage of small balls from inch up to 3 inches in diameter. At the completion of 76 hours the charge was of a uniform white color and all traces of the brown oxide had disappeared. The batch of lead used in this run was then washed and settlded by gravity in the usual manner. oar about four percent of uncorroded, coarse particles, so-called tailings" were produced, which is very low for a corrosion process, it being usual to get about ten percent tailings.

Tests made on the product of this particular batch were as follows:

Tinting power (white lead standard: 100) 150 Total plunger weight is 120 grams.

[1116 auto- It is understood that the sprinkling rates will white lead will be enabled to operate my process in view of the teaching that my process can take larger quantities of water than the usual prior art processes, particularly during the last steps of corrosion. Furthermore, the amounts of carbon dioxide introduced will also vary depending on conditions. Any skilled operator will realize that my process is not limited to the usual slow additions of carbon dioxide in order to produce a high yield as well as a. good finished product, the usual prior art processes being limited in this respect, it being further understood by anyone skilled in the art that the extent of carbonation can be varied to produce either a low carbonated lead, or if so desired, a high carbonated lead.

The foregoing description of my invention has been given for clearness and understanding. and no undue limitations are to be deduced there from.

I claim:

1. The process of producing white lead which comprises charging a lead oxide-finely divided tallic lea in w 10 e metallic lead content is present in an amount between about 10 percent and about 55 percent of the mixture total into. a. slowly revolving receptacle, introducing therein a gascontaining carbon dioxide, keeping the charge damp with water for an initial period of about from one to five hours, thereafter maintaining the dampened condition of the charge by the addition of a dilute acetic mgegglacid, then allowing the charge to c'orrode for a period of about thirty to fifty hours during which time the charge is kept dampened by the addition of water alone, and washing and drying the white lead thus produced.

2. The process of producing white lead which comprises charging a lead oxide-finely divided metallic lead mixture, in which the metallic lead content is present in an amount between about 25 percent and about 50 percent of the mixture total, into a cylinder, slowly revolving the said cylinder at the rate of about 9 revolutions per hour and introducing therein, at the rate of between about 25 and 40 cubic feet per minute, a gas containing between about 6 and 16 percent of carbon doxide, sprinkling the charge with water in amounts sufiicient to maintain the change in a moistened condition, once for each revolution for a period of about one to five hours, thereafter introducing into the sprink s stem for a period of about 20 hours a solution of "acetic acid of a strength of about 6 percent, sprinkling the same over the charge at the rate of about 1 to 1 quarts for each revolution of the cylinder, allowing the charge to corrode for a period of about 30 to 50 hours, during which time the charge is sprinkled with water alone at the rate of about 1 to 2 quarts per revolution, washing the white lead thus produced and drying the same.

EDWARD J. DUNN, JR.

2: 7 CERTIFICATE or. CORRECTION. Patent No.- 2,525,982. July 15, 1915.

EDWARD J. nmm, JR.

It is hereby certified. that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, line 51, claim 1, after "acetic" strike out "mineral";-line 14.8, claim z, for change read "charge"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record otthe case in the Patent Office.-

Signed. and sealed this 9th day of November, A. D. 1911.5.

Henry Van Aredale,

(Seal) Acting commissioner of Patents.