Process for the recovery of silver by flotation from the residue from the wet extraction of zinc

Ill AU9467435 (12) PATENT ABRIDGMENT (11) Document no AU-B-67435/94 (19) AUSTRALIAN PATENT OFFICE (10) Acceptance no. 667635 (54) Title PROCESS FOR THE RECOVERY OF SILVER BY FLOTATION FROM THE RESIDUE FROM THE WET EXTRACTION OF ZINC International Patent Classification(s) (51)^e C22B 007/00 0228 011/00 (21) Application No. : 67435/94 (22) Application Date : 12.07.9.4 (30) Priority Data (31) Number (32) Date (33) Country 4323339 13.07.93 DE GERMANY (43) Publication Date : 27.01.95' (44) Publication Date of Accepted Application : 28.03.96 (71) Applicant(s) METALLGESELLSCHAFTAKTIENGESELLSCHAFT (72) Inventor(s) ALI-NAGI BEYZAVI; HORST DITTMANN; FRIEDRICH ROSENgTOCK (74) Attorney or Agent WATERMARK PATENT & TRADEMARK ATTORNEYS , Locked Bag 5, HAWTHORN VIC 3122 (56) Prior Art Documents CA 1130258 AT 358290 (57) Claim 1. A process for the recovery of silver by flotation from the residue from the wet extraction of zinc, characterized in that the residue from the neutral wet extraction of zinc is recovered and is subsequently ground in an attritor and the residue which has been ground in an attritor is subjected to a flotation.

J B-jj.H/OU/Ull ZSlS/St "'FSgulalion 3.2(2) Australia""^wg ^ %j %JPatents Act 1990ORIGINALCOMPLETE SPECIFICATIONSTANDARD PATENT Application Number: Lodged: I Invention Title: PROCESS FOR THE RECOVERY OF SILVER BY FLOTATION FROM THE RESIDUE FROM THE WET EXTRACTION OF ZINC The following statement is a full description of this invention, including the best method of performing it known to us :- PROCESS FOR THE RECOVERY OF SILVER BY FLOTATION FROM THE RESIDUE FROM THE WET EXTRACTION OF ZINC DESCRIPTION This invention relates to a process for the recovery of silver by flotation from the residue from the wet extraction of zinc. The residue from the wet extraction of zinc contains silver mainly as AgaS. From Metallurgical Transactions B, Vol 19 B, October 1988 - 803, it is known that the residues from the neutral wet extraction of zinc which are obtained by Mitsubishi Akita can be subjected to a flotation with AC-404 at a pH from 3.5 to 4.0 to recover 80% of the originally present silver and some gold. It is also known from that publication that Zhuzhou recovers about 70% of the originally present silver by a flotation under acid conditions with the aid of a collector, which has not been specified. It is also known from that publication that Vieille Montagne has recovered about 90% of the originally present silver and about 75% of the originally present lead in two flotation concentrates by a flotation from residues from the acid wet extraction. The wet extraction of zinc is usually performed in one or two wet extraction stages. The neutral wet extraction of zinc is usually performed at a slightly acid pH. The second wet extraction stage is performed at an acid pH. In many cases the second extraction stage is not performed owing to its poor economy. It is an object of the invention to provide for the recovery of silver from the residue from the wet extraction of zinc an economical flotation process which results in a maximum yield of silver. The object of the invention is accomplished in that the residue from the neutral wet extraction if zinc is recovered and is subsequently ground in an attritor and the residue which has been ground in an attritor is subjected to a flotation. The combination of grinding in the attritor and flotation in accordanqe with the invention results in a recovery of silver concentrates containing 2 to 2.6 g/kg silver from a residue having a silver content of 0.245 g/kg. The process in accordance with the invention results in a silver yield of > 89.5%. When the residue from the neutral wet extraction of zinc has been ground in the attritor, it has a_r large surface area. In accordance with the invention the metal values of that residue are separated by flotation. In the attritor the surfaces of the grains are subjected to attrition so that silver-containing crusts present on the surfaces of the grains are detached. The flotation of the residue from the neutral wet extraction of zinc will result in higher silver concentrations and a higher silver yield when the residue has previously y been ground in an attritor. The flotation is effected in a manner known per se in that the residue which has been ground in an attritor is suspended in water and after an addition of collectors the suspension is conditioned by stirring, whereafter frothing agents are added and air is supplied at a controlled rate. According to a particularly preferred feature of the invention the residue from the rveutral wet extraction of zinc is treated in a drum which contains grinding media comprising 20 to 30 % by volume of media having a particle size < 30 mm and which has a net energy input of 2 to 10 kWh per 1000 kg of the throughput. The attrition performed in accordance with the invention may be performed in a baf! mill or vibrating ball mill or by means of attriting stirrers. The net energy input to the drum of a given mill is the energy which is transmitted to the shell of the drum, i.e., the energy input to the filled drum minus the energy input to the empty drum. The net energy input is related to the throughput of dry residue. Owing to that grinding in an attritor performed in accordance with the invention it has been possible td recover silver concentrates which had a particularly high silver content and to achieve a particularly high yield of silver. According to a preferred feature of the invention the surface area of the grains is increased by 50 to 60 % in that the residue of the neutral wet extraction of zinc i§ ground in an attritor. As the residue is ground in accordance with the invention in an attritor, grains having a very large surface area are obtained because th6 silver* eontaining crusts are abraded from the surfaces of the grains. The mechanical detaching of the silver-containing crusts results in a particularly high silver yield ^ The invention will be explained with reference to the examples. Residues were used which were obtained by the neutral wet extraction of zinc. The material contained 48% by weight water and had a d50 value of 7.9 micrometers and a d80 value of 19 micrometers. The residue contained 0.245 silver per kg. The most important components of the residue were 3.4% by weight Pb, 19.0% by weight Zn, 1.7% by weight Cu, 26.7% by weight Fe and 4.5% by weight S. The contents of said components in % by weight are based on the dry residue. The attrition was effected in a ball mill. The net energy input to the drum was of an order of 10 kWh per 1000 kg throughput. During this flotation the pH value was adjusted with H₂S0₄. Potassium amyl xanthate was used as a collector in an amount of about 0.6 g/kg. The suspension was conditioned by stirring. A modified pine oil was used as a frothing agent. As is apparent from the following Table I the residue from the neutral wet extraction of zinc was fine-grained. It is also apparent from Table I that the particle size was not considerably changed by the attriting, however, the surface area of the grains of the residue was increased by 53%. TABLE I dso d50 Specific Surface areas mm_______mm_______cm^/g_______..... Residue without attrition 0-019 0.0079 7470 after attrition 0.0166 0.0076 11460 1)produced by Hoechst AG 2) Fisher Sub-sieve Sizer The flotation was performed in each case with a slurry which contained 300 g/l solids. A collector was added to the slurry in an amount of 600 g per 1000 kg of solids. Conditioning was effected by stirring for about 5 minutes. Frothing agent was added to the suspension in an amount of 30 g per 1000 kg solids. Air was supplied at a rate of 60 sma (sm^ = standard cubic meter) per hour and per m* cell contents. The flotation time was about 7 minutes. During that time air was supplied and the resulting froth was continuously withdrawn.

^w- From the example for a "Flotation After Attrition" reported in the Table it is apparent that the yield of silver in the froth (1) amounted to 89.8% of the silver in the feed. 10.2% of the silver in the feed were measured in the underflow. It is also apparent from the example that the feed contained 245 g silver per 1000 kg. A silver concentration of 2000 g/1000 kg was measured in the froth (1) and a silver concentration of 28g/T000 kg in the underflow (1). In the example the concentration of the silver in the froth (1) was 8.2 times the silver concentration in the feed. But the essential advantage resides in that the yield of silver in the froth (1) amounted to 89.8%. From the control example "Flotation of Silver Without Preceding Attrition" it is apparent that the amount of silver in the froth (1) was only 16% of the amount of silver in the feed. 84.0% of the silver content of the feed were detected in the underflow (1). It is also apparent from the control example that the feed contained 245 g silver per 1000 kg. The froth (1) had a silver content of 885 g per 1000 kg; this corresponded to an increase of the silver concentration only by the factor 3.6 EXAMPLE: Flotation After Attrition Metal Content? Product Wt.% Pb Zn Cu% Fe As S g/1000kg Ag Froth(l) 11.0 2.8 26.0 2.6 22.9 0.29 9.8 Underflow(l) 89.0 3.2 18.7 1.7 27.3 0.43 4.32 Froth (2) 20.9 3.6 19.0 1.7 27.8 0.40 4.4 - Underflow(2) 68.1 3.5 18.6 1.7 27.2 0.40 4.3 - Feed too.o 3.4 19.5 1.8 26.8 0.38 4.93 Product Wt.% Pb Zn Cu% Fe As S g/1000kg Ag Froth(l) 11.0 2.8 26.0 2.6 22.9 0.29 9.8 Underflow(l) 89.0 3.2 18.7 1.7 27.3 0.43 4.32 Froth (2) 20.9 3.6 19.0 1.7 27.8 0.40 4.4 - Underflow(2) 68.1 3.5 18.6 1.7 27.2 0.40 4.3 - Feed too.o 3.4 19.5 1.8 26.8 0.38 4.93 Yield (%) Product Pb Zn Cu Fe As S Ag Froth (1) 9.0 14.7 16.0 9.3 7.9 21.9 89.8 Underflow (2) 91.0 85.3 84.0 90.7 92.1 78.1 10.2 Froth (2) 21.9 20.4 19.9 21.6 21.1 18.7 - Underflow (2) 69.1 64.9 64.1 69.1 71.0 59.4 * Feed 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Product Pb Zn Cu Fe As S Ag Froth (1) 9.0 14.7 16.0 9.3 7.9 21.9 89.8 Underflow (2) 91.0 85.3 84.0 90.7 92.1 78.1 10.2 Froth (2) 21.9 20.4 19.9 21.6 21.1 18.7 - Underflow (2) 69.1 64.9 64.1 69.1 71.0 59.4 * Feed 100.0 100.0 100.0 100.0 100.0 100.0 100.0 CONTROL EXAMPLE: FLOTATION WITHOUT A PRECEDING ATTRITION Metal Contents Product Wt.% %Pb %Zn %Cu %Fe %As %S g/1000kg Ag Froth (1) 4.4 2.1 34,2 1.8 18.4 0.24 16.3 Underflow (1) 95.6 3.4 1.6 1.7 27.1 0.36 3.5 Froth (2) 16.9 6.0 7.0 3.1 24.9 0.33 6.0 - Underflow (2) 78.7 2.9 19.7 1.4 27.6 0.45 3.0 - Feed 100.0 3.4 19.9 1.7 26.7 0.42 4.09 Product Wt.% %Pb %Zn %Cu %Fe %As %S g/1000kg Ag Froth (1) 4.4 2.1 34,2 1.8 18.4 0.24 16.3 Underflow (1) 95.6 3.4 1.6 1.7 27.1 0.36 3.5 Froth (2) 16.9 6.0 7.0 3.1 24.9 0.33 6.0 - Underflow (2) 78.7 2.9 19.7 1.4 27.6 0.45 3.0 - Feed 100.0 3.4 19.9 1.7 26.7 0.42 4.09 Yield, (%) Product Pb Zn Cu Fe As S Ag Froth (1) 2.7 7.5 4.7 3.0 2.4 17.6 16.0 Underflow (1> 97.3 92.5 95.3 97:0 97.6 82.4 84.0 Froth (2) 29.9 14.6 30.6 15.7 14.3 24.7 * Underflow (2) 67.4 77.9 64.7 81.3 83.3 57.7 - Feed 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Product Pb Zn Cu Fe As S Ag Froth (1) 2.7 7.5 4.7 3.0 2.4 17.6 16.0 Underflow (1> 97.3 92.5 95.3 97:0 97.6 82.4 84.0 Froth (2) 29.9 14.6 30.6 15.7 14.3 24.7 * Underflow (2) 67.4 77.9 64.7 81.3 83.3 57.7 - Feed 100.0 100.0 100.0 100.0 100.0 100.0 100.0 THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1.A process for the recovery of silver by flotation from the residue from the wet extraction of zinc, characterized in that the residue from the neutral wet extraction of zinc is recovered and is subsequently ground in an attritor and the residue which has been ground in an attritor is subjected to a flotation. 2.A process according to claim 1, characterized in that the residue from the neutral wet extraction of zinc is treated in a drum which contains grinding media comprising 20 to 30 % by volume of media having a particle size < 30 mm and which has a net energy input of 2 to 10 KWh per 1000 kg of the throughput. 3.A process according to claim 1 or 2, characterized in that the surface area of the grains is increased by 50 to 60 % in that the residue of the neutral wet extraction of zinc is ground in an attritor. DATED this 11th day of July 1994. MFTALLGESH I SCHAFT AttTIFNIftFSFLLSCHAFT WATERMARK PATENT & TRADEMARK ATTORNEYS THE ATRIUM 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA 7 ABSTRACT In a process for the recovery of silver by flotation from the residue from the wet extraction of zinc, the residue from the neutral wet extraction of zinc is recovered and is subsequently ground in an attritor and the residue which has been ground in an attritor is subjected to a flotation.