GB1576497A

GB1576497A - Lead chloride preparation

Info

Publication number: GB1576497A
Application number: GB14397/77A
Authority: GB
Original assignee: Compagnie Royale Asturienne des Mines
Current assignee: Compagnie Royale Asturienne des Mines
Priority date: 1976-04-06
Filing date: 1977-04-05
Publication date: 1980-10-08
Also published as: JPS52145396A; DE2712567A1; BE853314A; FR2347310B3; FR2347310A1; CA1113224A; ES457544A1; SE7703978L; NL7703184A; IT1082485B; SE415559B

Description

(54) LEAD CHLORIDE PREPARATION (71) We, COMPAGNIE ROYALE ASTURIENNE DES MINES, a Belgian Body Corporate, of Place de la Liberte, Brussels, Belgium, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention relates to a process for preparing commercially pure lead chloride from lead carbonate or sulfate containing metallic impurities such as copper and silver.

Certain industrial uses of lead salts require a degree of purity, at least with respect to certain specific impurities, very much greater than the degree of purity possible with lead salts prepared from plumbous ores by known industrial processes. It is then necessary, for the foregoing to use lead salts of high purity which are very costly. For example in the production of polyvinyl chloride, basic lead sulfate may be used as a stabilizer. Yet such basic lead sulfates must contain no more than a few ppm of silver or copper as they act as catalysts speeding the deterioration of the polyvinyl chloride. Now, lead ores or plumbous ores always contain copper and silver in quantities sufficient for basic lead sulfates prepared industrially therefrom to have amounts of copper and silver much greater than the quantities permitted.

Moreover, certain foreign metals deleterious to particular uses of lead salts have an intrinsic value which may in itself justify recovery.

An object of the invention is the provision of a process of preparing commercially pure lead chloride from lead carbonate or lead sulfate containing unacceptable quantitues of foreign metals.

Another object of the invention provides a process for preparing commerciallly pure lead chloride wherein some foreign metals are separated in a form enabling economic recovery.

Accordingly the invention provides a process of preparing commercially pure lead chloride from lead carbonate or lead sulfate containing metal impurities such as copper or silver comprising leaching at elevated temperature the lead sulphate or lead carbonate with an aqueous solution of calcium chloride and hydrochloric acid, filtering at elevated temperature the insoluble substances from the leaching liquor, cooling the separated liquor thereby to obtain crystalline lead chloride, and filtering and washing the crystallized lead chloride from the cooled liquor, and collecting lead depleted filtrate resulting from the filtering and washing of the crystallised lead chloride.

Indeed, lead chloride is far more soluble at higher rather than lower temperatures, whereas chlorides of other metals which are likely to accompany the lead in the treated salts have solubilities which vary little with temperature.

The leaching of lead sulfate occurs according to the following reaction:

The leaching of lead carbonate occurs according to the following reaction:

The solubilization of lead chloride at elevated temperature is favored by the presence of hydrochloric acid in reaction (1) and by the presence of calcium chloride in reaction (2).

Moreover, in an acid medium, the excess Cl ions enable the solubilization of the silver in the form of complex ion Ag Cin (nç Preferably, the leaching solution contains 100 to 500 g/l of calcium chloride and 5 to 150 g/l of hydrochloric acid.

Preferably, the leaching step is repeated on the separate insoluble substances until the insoluble substances in the lead have been substantially entirely eliminated. The leaching step is preferably carried out in the vicinity of the boiling point and the separated liquor is cooled down to about ambient temperature. The greater the temperature difference between the temperatures of leaching and crystallization of lead chloride the greater is the recovery yield.

Of advantage is following up the high temperature filtration step with a high temperature washing step, e.g. by washing with hot water, so as not to leave any lead chloride in the insoluble substances.

It is likewise advantageous to prepare leaching solution from separated leaching liquor or filtrate by adding measured amounts of calcium chloride and hydrochloric acid. The recycling of solutions after readjusting their concentrations minimizes losses of lead chloride and enriches the solutions in foreign metals.

When the lead-depleted filtrate contains a sufficient amount of foreign metals, at least a part is drawn off which is neutralized with milk of lime in order to precipitate the oxides or hydroxides of foreign metals. It is preferable to neutralize up to a pH of 9. The metal oxide precipitates may be treated by known processes for separating metal having a high intrinsic value, like silver.

Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawing which shows a flow diagram of the various steps of a process according to the invention.

According to the preferred illustrated arrangement a heated digester 1 is provided into which lead sulfate or lead carbonate is introduced together with an aqueous digesting or leaching solution prepared in unit 2 containing calcium chloride and hydrochloric acid of the desired concentration. After leaching in the digester 1 the resulting pulp is discharged into a filter 3 which is heated and washing water is added. The filtrate leaving the filter 3 may be carried via the two-way valve 4 for preparation of leaching solution in unit 2 or to a cooled crystallizer 6. The insoluble substances separated by filtration in the filter 3 may be conveyed to the digester 1 or eliminated, depending on the position of the two-way valve 5.

The contents of the crystallizer 6 may be discharged on the filter 7 together with an inflow of washing water. The filtrate leaving the filter may be conveyed by means of the two-way valve 8 to the leaching solution preparation unit 2 or to the neutralization tank 9, together with an inflow of milk of lime. The contents of the neutralization tank is discharged into the filter 10. The filtrate is eliminated and the solids separated.

The leaching solution is prepared in the unit 2 so that the amount of calcium chloride is between 100 and 500 g/l and the amount of hydrochloric acid is between 5 and 150 g/l. The leaching in the digester 1 puts into solution, as chlorides, the lead and the metal impurities (viz. copper and silver, the silver being in the form of the ion complex Ag Cln (n-1)-). After filtration in the filter 3, if the insoluble substances contain no more than a trace of lead, they are washed at elevated temperature then eliminated, if the insoluble substances still contain a not inconsiderable amount of lead they are returned to the digester 1 for further leaching.

If the amount of lead chloride in the leaching liquor is high the liquid is conveyed to the crystallizer 6; if the amount of lead chloride in the leaching liquor is low, namely after leaching of insoluble substance already depleted in lead, the liquor is carried to the leaching preparing unit 2 where the concentration of calcium chloride and hydrochloric acid are adjusted in order to reestablish the initial concentrations of the leaching solution.

The leaching liquor carried to the crystallizer is cooled down to about ambient temperature. Lead chloride precipitates and is recovered by filtering and washing in the filter 7. So long as the filtrate contains small amounts of foreign metals, it is recycled to be regenerated into leacing solution whose concentration of calcium chloride and hydrochloric acid is readjusted. On the other hand, when the concentration of the foreign metals becomes large enough to interfere with the leaching of the lead salt, or permit economic recovery of the foreign metals themselves, at least part of the filtrate is conveyed to the neutralizing tank 9.

Milk of lime is then added to neutralizing tank 9 to raise the pH and precipitate the oxides and hydroxides of foreign metals contained therein. The oxides or hydroxides are separated by filtration. If the amount metal has a high enough intrinsic value to warrant, the foreign metals may be isolated by known processes.

The present invention is further illustrated by the following Examples: EXAMPLE 1 Starting with a lead sulfate solution whose composition is as follows: Pb . . . ..65 % by weight Ag... ......... ..... ... ... .......660 g/T (ppm) 24 g of lead sulfate of the above composition were leached with 500 cc of solution containing: CaCl2 . ..160 g HCl . ..10 cu.cm. at 22.22 Bé The temperature is held at 1000C for two hours. The pulp was then filtered hot which made it possible to recover a solid substance containing 30 % by weight more lead. The lead chloride was crystallized by cooling the filtrate to 200C. It was then filtered and washed.

The analysis of the lead chloride was as follows: Pb......................................72.1% by weight Ag ...................................... < 5 g/T Cl ......................................22.8% by weight SO4...................................... 1.23% by weight Ca ...................................... 0.56% by weight The solid leaving the preceding leaching step was leached once again with the solution obtained after crystallization. Beforehand the solution of calcium chloride and hydrochloric acid was increased to the starting amount of 500 cu.cm. The composition of the solution was: CaCl2 ...................................160 g HCl ..................................... 10 cu.cm. at 22.2 Bé The second leaching operation was conducted at 1000C for two hours.The pulp was filtered hot which allowed 7.7 g of solid material to be collected containing more than 4%by weight of lead and 30 g/T (ppm) silver. These figures make it possible to calculate the solubilization yield of lead (98%) and silver (99%). The filtrate obtained from the second leaching operation without previous crystallization of the lead chloride, so as to leach 24 g of lead sulfate. The double leaching of lead sulfate with the intermediate crystallization operation produced the same results as above relative to the solubilization yield and the composition of the lead chloride.

EXAMPLE 2 The starting substance was natural lead carbonate containing 71.85 %, by weight, lead, 255 g/T silver and 0.95% by weight, copper.

24 g of lead carbonate was leached with 500 cu.cm of solution containing: CaCl2 . ... .... ., 160 g HCl..................................... 20 cu.cm. at 22.2 Bé The temperature was held at 100 C for fifteen minutes. The pulp was filtered hot and 0.9 g of solid material was collected containing: Pb.. ...... ....... ..... . ..26.4% by weight SiO2 ... . .... ....... ...10.4% by weight Ag.................... .................60 g/T (p.p.m.) Calculations show that the solubilization yield reached 98.5%forthe lead and 99%for the silver.

The lead chloride was collected by cooling the filtrate to 200 C.

After filtration and washing the analysis of the lead chloride was as follows: Pb . . . . . ..... ........72.2% by weight Cl . . . ..... . . . 22.9% by weight Ca . ..... . . . . 0.2% by weight SO4 .. . . . . .. . . .. 2.13% by weight Ag . . .... . . ........... < 5 g/T (p.p.m.) Cu . ..... .............................. < 0.001% by weight After crystallization sufficient quantities of hydrochloric acid and calcium chloride were added to the remaining leaching solution to obtain the concentration of the initial solution so as to leach 24 g of lead carbonate as set out in the preceding example.

EXAMPLE 3 After crystallization of the starting solution and separation of the lead chloride five treatment cycles, with 24 g of lead sulfate in each cycle, were carried out. The steps were carried out under the same conditions as given Example 1.

The solution contained: Pb . 5 g/l Ag.................... .................0.140 g/l By neutralizing the solution with a 30% solution of milk of lime so that the final pH was equal to 9 there was obtained a solution containing 0.160 g/l of lead and 0.0005 g/l of silver and a precipitate containing 30.75% lead and 10 kg/T silver.

WHAT WE CLAIM IS 1. A process of preparing commercially pure lead chloride from lead sulfate or lead carbonate containing metal impurities such as copper and silver, comprising leaching lead sulfate or lead carbonate at elevated temperature with an aqueous leaching solution of calcium chloride and hydrochloric acid, filtering at elevated temperature the insoluble substances from the resulting leaching liquor, cooling the separated leaching liquor thereby to obtain crystalline lead chloride, filtering and washing the crystallized lead chloride from the cooled liquor, and collecting lead-depleted filtrate resulting from the filtration and washing of the crystallised lead chloride.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

The temperature is held at 1000C for two hours. The pulp was then filtered hot which made it possible to recover a solid substance containing 30 % by weight more lead. The lead chloride was crystallized by cooling the filtrate to 200C. It was then filtered and washed.

The analysis of the lead chloride was as follows: Pb......................................72.1% by weight Ag ...................................... < 5 g/T Cl ......................................22.8% by weight SO4...................................... 1.23% by weight Ca ...................................... 0.56% by weight The solid leaving the preceding leaching step was leached once again with the solution obtained after crystallization. Beforehand the solution of calcium chloride and hydrochloric acid was increased to the starting amount of 500 cu.cm. The composition of the solution was: CaCl2 ...................................160 g HCl ..................................... 10 cu.cm. at 22.2 Bé The second leaching operation was conducted at 1000C for two hours.The pulp was filtered hot which allowed 7.7 g of solid material to be collected containing more than 4%by weight of lead and 30 g/T (ppm) silver. These figures make it possible to calculate the solubilization yield of lead (98%) and silver (99%). The filtrate obtained from the second leaching operation without previous crystallization of the lead chloride, so as to leach 24 g of lead sulfate. The double leaching of lead sulfate with the intermediate crystallization operation produced the same results as above relative to the solubilization yield and the composition of the lead chloride.

EXAMPLE 2 The starting substance was natural lead carbonate containing 71.85 %, by weight, lead, 255 g/T silver and 0.95% by weight, copper.

24 g of lead carbonate was leached with 500 cu.cm of solution containing: CaCl2 . ... .... ., 160 g HCl..................................... 20 cu.cm. at 22.2 Bé The temperature was held at 100 C for fifteen minutes. The pulp was filtered hot and 0.9 g of solid material was collected containing: Pb.. ...... ....... ..... . ..26.4% by weight SiO2 ... . .... ....... ...10.4% by weight Ag.................... .................60 g/T (p.p.m.) Calculations show that the solubilization yield reached 98.5%forthe lead and 99%for the silver.

The lead chloride was collected by cooling the filtrate to 200 C.

After filtration and washing the analysis of the lead chloride was as follows: Pb . . . . . ..... ........72.2% by weight Cl . . . ..... . . . 22.9% by weight Ca . ..... . . . . 0.2% by weight SO4 .. . . . . .. . . .. 2.13% by weight Ag . . .... . . ........... < 5 g/T (p.p.m.) Cu . ..... .............................. < 0.001% by weight After crystallization sufficient quantities of hydrochloric acid and calcium chloride were added to the remaining leaching solution to obtain the concentration of the initial solution so as to leach 24 g of lead carbonate as set out in the preceding example.

EXAMPLE 3 After crystallization of the starting solution and separation of the lead chloride five treatment cycles, with 24 g of lead sulfate in each cycle, were carried out. The steps were carried out under the same conditions as given Example 1.

The solution contained: Pb . 5 g/l Ag.................... .................0.140 g/l By neutralizing the solution with a 30% solution of milk of lime so that the final pH was equal to 9 there was obtained a solution containing 0.160 g/l of lead and 0.0005 g/l of silver and a precipitate containing 30.75% lead and 10 kg/T silver.

WHAT WE CLAIM IS 1. A process of preparing commercially pure lead chloride from lead sulfate or lead carbonate containing metal impurities such as copper and silver, comprising leaching lead sulfate or lead carbonate at elevated temperature with an aqueous leaching solution of calcium chloride and hydrochloric acid, filtering at elevated temperature the insoluble substances from the resulting leaching liquor, cooling the separated leaching liquor thereby to obtain crystalline lead chloride, filtering and washing the crystallized lead chloride from the cooled liquor, and collecting lead-depleted filtrate resulting from the filtration and washing of the crystallised lead chloride.
2. A process according to Claim 1, wherein the leaching solution contains from 100 to

500 g/l of calcium chloride and from 5 to 150 g/l hydrochloride acid.
3. A process according to Claim 1 or 2, wherein the filtered out insoluble substances are leached again until the lead in the insoluble substances has been eliminated.
4. A process according to any of Claims 1 to 3, wherein the leaching step is carried out at a temperature in the vicinity of the boiling point of the leaching mass.
5. A process according to any one of Claims 1 to 4, wherein the elevated temperature filtration of the insoluble substances is followed by washing of the separated substances with hot water.
6. A process according to any of the preceding claims, wherein the separated leaching liquor is cooled down to above ambient temperature.
7. A process according to any of the preceding claims, comprising preparing a leaching solution from the leaching liquor by adding measured amounts of calcium chloride and hydrochloric acid to obtain a desired concentration.
8. A process according to any of Claims 1 to 6, further comprising preparing the leaching solution from collected lead-depleted filtrate by adding thereto measured amounts of hydrochloric acid and calcium chloride.
9. A process according to any of the preceding claims, further comprising neutralizing with milk of lime at least part of the collected lead depleted filtrate and separating metal oxides precipated therefrom.
10. A process according to Claim 9, wherein the neutralizing step is carried out at a pH of up to 9.
11. A process according to Claim 9 or 10, comprising treating the precipated metal oxides to recover at least some of the metals contained therein.
12. A process of preparing commercially pure lead chloride from lead sulfate of carbonate substantially as herein described with reference to the accompanying drawing.
13. Commercially pure lead chloride prepared by a process according to any one of the preceding claims.