AU652231B2 - Oxidation of metal sulfides using thermotolerant bacteria - Google Patents

Description

(21) International Application Number: PCT/AU92/00117 (22) International Filing Date Priority data: PK 5204 20 March 1992 (20.03.92) 22 March 1991 (22.03.91) (71) Applicant (for all designated States except US): BAC TECH (AUSTRALIA) PTY. LTD. [AU/AU]; 1st Floor, 49 Stirling Highway, Nedlands, W.A. 6009 (AU).

(72) Inventors; and Inventors/Applicants (for US only) SPENCER, Peter, Andrew [AU/AU]; 21 Camm Avenue, Bullcreek, W.A. 6153 BUDDEN, Julia, Rose [AU/AU]; 24 Saturn Street, Beckenham, W.A. 6107 BARRETT, Jack [GB/GB]; 273 Kings Road, Kingston Upon Thames, Surrey KT2 5JJ HUGHES, Martin, Neville [GB/ GB]; 25 Lynwood Heights, Rickmansworth, Herts WD3 4ED POOLE, Robert, Keith [GB/GB]; 15 Ernmore Road, Putney, London SW15 6LL (GB).

(74) Agent: LORD, Kelvin, Ernest; 4 Douro Place, West Perth, W.A. 6005 (AU).

(81) Designated States: AT, AT (European patent), AU, BB, BE (European patent), BF (OAPI patent), BG, BJ (OAPI patent), BR, CA, CF (OAPI patent), CG (OAPI patent), CH, CH (European patent), CI (OAPI patent), CM (OAPI patent), CS, DE, DE (European patent), DK, DK (European patent), ES, ES (European patent), FI, FR (European patent), GA (OAPI patent), GB, GB (European patent), GN (OAPI patent), GR (European patent), HU, IT (European patent), JP, KP, KR, LK, LU, LU (European patent), MC (European patent), MG, ML (OAPI patent), MN, MR (OAPI patent), MW, NL, NL (European patent), NO, PL, RO, RU, SD, SE, SE (European patent), SN (OAPI patent), TD (OAPI patent), TG (OAPI patent), US.

Published With international search report.

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i*31 s a (54) Title: OXIDATION OF METAL SULFIDES USING THERMOTOLERANT BACTERIA (57) Abstract A process for recovering precious or base metals from particulate refractory sulfide materials comprises: a) contacting the sulfide material with an aqueous solution containing a thermotolerant bacteria culture capable of promoting oxidation of the sulfide material at a temperature in the range from 25 to 55 b) separating the oxidized residue from the aqueous liquid, and, c) treating the oxidized residue and/or the aqueous liquid to recover metal. In this context, a thermotolerant bacterium is one which has an optimum growth temperature of 40 to 45 oC, and an operating temperature of 25 to 55 °C.

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WO 92/16667 PCT/AU92/00117 14 The thermotolerant bacteria culture MTC 1 was isolated from W ct4avn &ncr-a 1 :lrlf i^ r.rl c i c~

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WO 92/16667 PCT/AU92/00117 1

TITLE

OXIDATION OF METAL SULFIDES USING THERMOTOLERANT BACTERIA

DESCRIPTION

The present invention relates to a process for the treatment of metal containing materials by bacterial oxidation.

FIELD OF THE INVENTION It is known that recovery of metals especially precious metals and base metals from refractory sulphide materials can be enhanced by bacterial oxidation or leaching, The bacterial treatment subjects the sulphide material to a pre-oxidation. The refractory sulphide materials can take a wide variety of forms including mineral sulphides, carbonaceous sulphide ores, sulphide flotation .concentrates, sulphide gravity concentrates, sulphide tailings, sulphide mattes and sulphidic fume.

The precious metals and some base metals remain in the oxidised solid residue and can be recovered by conventional carbon in pulp or other chemical leaching processes. Some base metals such as copper, zinc and nickel go into solution and may be recovered directly by conventional solvent extraction and electrowinning.

In the past, bacterial oxidation of precious or base metal containing sulphide materials has typically been conducted 25 using bacteria of the Thiob-cillus species. However, the Thiobacillus species can only operate at temperatures up to about 40°C. Further, the oxidation effected by Thiobacillus bacteria is an exothermic reaction and it is sometimes necessary to cool the process reactors to prevent i

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i:: 1 rii j; 1 :1 ~b _LJI WO92/16667 PCT/AU92/00117 -2the temperature exceeding that at which the Thiobacillus bacteria can operate.

SUMMARY OF THE INVENTION The present invention provides a process for the bacterial oxidation of metal containing sulphide materials using thermotolerant bacteria which can operate at higher temperatures than conventional Thiobacillus bacteria.

In accordance with one aspect of the present invention there is provided a process for recovering metals from particulate refractory precious or base metal containing sulphide materials which comprises contacting the sulphide material with an aqueous solution containing a thermotolerant bacteria culture (as herein defined) capable of promoting oxidation of the sulphide material at a temperature in the range from 25 to 55 0 C, separating the oxidised residue from the aqueous liquid and treating the oxidised residue and/or the aqueous liquid to recover metal therefrom.

DESCRIPTION OF THE INVENTION The thermotolerant bacteria used in the present invention are as described in "Thermophiles General, Molecular, and Applied Microbiology" edited by Thomas D. Brock and published by John Wiley Sons (1986). In Chapter 1 of this publication, there is illustrated in Figure 1(b) a graph showing that thermotolerant bacteria grow at temperatures lower than those preferred by moderate and obligate or extreme thermophiles.

In the context of the present invention, a thermotolerant bacteria is one which has an optimum growth temperature of -51t- II WO 92/16667 PCT/AU92/00117 -3to 45°C and an operating temperature of 25 to Preferably, the aqueous solution used in the process of the present invention is acidic. It has been found that the optimum acidity of the aqueous liquid for growth of the thermotolerant bacteria culture used in the present invention is in the range from pH 1.3 to 2.0, whilst the optimum acidity of the aqueous liquid for operation of the process of the present invention is in the range from pH to The bacterial oxidation step of the process of the present invention is conducted in the presence of nutrients which are typically dissolved salts of nitrogen, potassium and phosphorus. The nutrients may already be present in the aqueous liquid or they may be added thereto. The nutrient materials promote the growth of the thermotolerant bacteria.

It is preferred that the thermotolerant bacteria be acidophilic in view of the pH conditions'under which the process of the present invention is preferably conducted.

Further, the thermotolerant bacteria used in the process of the present invention are typically aerobic and thus the aqueous liquid is preferably aerated during the operation of the process to ensure that there is an adequate supply of oxygen for the bacteria. Still further, it is found that the thermotolerant bacteria culture used in the process of the present invention is typically capable of autotrophic growth. Yet further, the thermotoleranti bacteria culture typically does not require additional

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2 over and above that normally available from ambient air.

The thermotolerant bacteria culture used in the process of the present invention may be capable of oxidising arsenic (III) to arsenic in acidic aqueous solutions containing soluble iron salts. Further, the thermotolerant bacteria culture used. in the process of the present invention may be capable of oxidising iron (II) to iron (III) in acidic aqueous solutions and may be capable of oxidising reduced sulphur species to sulphate ion in acidic aqueous solutions.

Also, the thermotolerant bacteria culture used in the process of the present invention is preferably capable of oxidising iron and sulphides in an aqueous liquid containing up to 20 grams/litre of sodium chloride without the addition of special nutrients or employment of the special conditions. Thus, in this case extracting the pH, temperature, oxygen, nitrogen phosphate and potassium levels are maintained as discussed above, oxidation will proceed.

Typically, a particular culture of thermotolerant bacteria contains one or more bacteria species.

The process of the present invention can be operated in heaps, dumps, agitated systems or dams.

After completion of the oxidation step the oxidised solid residue and the aqueous liquid are typically separated. In the case of precious metal recovery, the oxidised solid residue would preferably be washed and then the pH of the oxidised solid residue adjusted to a level compatible with the use of a cyanide leaching agent. Alternatively,,

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l- c L Inftmutn Appiautio. No. PCTMU !2i01 V1 US,A,4752332 (WU et al.) 21 June 1988 (21.06.88).

Sea column 7, lines 7.24.

(1-9) S WO 92/16667 PCT/AU92/00117 another reagent such as thiourea could be used under acidic conditions and so the need to adjust the pH is obviated.

EXAMPLES

The present invention will now be illustrated by the following examples.

EXAMPLE 1 A pyrite gold concentrate designated P 1 was treated in accordance with the present invention. The concentrate contained pyrite as the major sulphide mineral with minor amounts of chalcopyrite, sphalerite, galena and arsenopyrite. Other minerals present were quartz, sericite and siderite.

The concentrate had the following assay.

Table 1 Assay of Pyrite Concentrate P 1 Element Symbol Assay (by weight) Gold Au 52.0 ppm Iron Fe 26.0% Sulphur S 27.5% Nickel Ni 113 ppm Copper Cu 880 ppm.

4 Zinc Zn 320 ppm Lead Pb 160 ppm Arsenic As 3750 ppm, Silver Ag 8 ppm Samples of the concentrate were mixed with a sulphuric acid solution a a pulp density of 3% w/w to provide a pH range of 1.2 to 1.5. Nutrients included in the acid solution 4 S Iiwere ammonium sulphate at 200 mg/L, di-potassium hydrogen phosphate at 200 mg/L and magnesium sulphate heptahydrate at 400 mg/L.

The acid level (pH) may vary from the start value and may either rise and then fall or fall from the outset. In most tests, the variation can be significant with the final pH often less than The slurry was inoculated with a thermotolerant bacteria culture designated MTC 1. The inoculated slurry was shaken in conical flasks at a temperature of 43 0 C. Samples were removed periodically and analysed for iron and arsenic extraction to determine the progress of the treatment.

The sample was treated by bacterial oxidation for 30 days to achieve 80% oxidation of the pyrite mineral. The solids weight loss due to the oxidation process was 52%. The solid residue was then separated from the residual acid solution. Leaching of the solid residue using alkaline cyanide solution recovered 92% of the gold. In comparison, cyanide leaching could recover only 74% of the gold from the concentrate in the untreated state. These results are summarised in Table 2.

Table 2 Gold Recovery from Untreated and Oxidised Concentrate SSample Iron Extracted Gold Recovered (by weight) By Cyanide :i Leaching (by i weight) I 'Untreated 0% 74% i Bacterial 80% 92% Ado

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Oxidation The cyanide solution employed to recover the gold contained sodium cyanide at a concentration of 2 g/L.

The iron in the solution from the bacterial oxidation process can be removed by adjusting the pH to above 5.0 by the addition of lime, limestone, alkaline tailings or sodium hydroxide.

The results of this test show that gold encapsulated with pyrite (FeS) can be released from the sulphide lattice by at least partial oxidation of the sulphur and iron by the thermotolerant bacteria culture MTC 1 to render the gold accessible to cyanide solution.

EXAMPLE 2 A nickel sulphide ore designated N 1 was treated in accordance with the present invention. The ore contained both sulphidic nickel and non-sulphidic nickel minerals including violarite, lizardite and niccolite (NiAs).

Approximately 70% of the nickel was present as sulphidic nickel. Other minerals were siderite, goethite, pyrite, chlorite and quartz.

The ore had the following assay.

Table 3 Assay of Nickel Ore N 1 Element Symbol Assay (by weight) Nickel Ni 2.74% Iron Fe 18.7% Samples of the ore were mixed with a sulphuric acid solution at a pulp density of 13% w/w to provide a pH range of 1.2 to 1.5\ Nutrients included in the acid solution ~0 WO 92/16667 PCT/AU92/00117 8 were ammonium sulphate at 200 mg/L, di-potassium hydrogen phosphate at 200 mg/L and magnesium sulphate heptahydrate at 400 mg/L.

The acid level (pH) may vary from the start value and may either rise and then fall or fall from the outset. In most tests, the variation can be significant with the final pH often less than The slurry was inoculated with the thermotolerant bacteria culture designated MTC 1. The inoculated slurry was shaken in conical flasks at a temperature of 47 0 C. Samples were removed periodically and analysed for iron and nickel extraction to determine the progress of the treatment.

At the completion of the bacterial oxidation treatment, 17 days, the solution was removed from the residual solids and the residual solids washed with sulphuric acid solution to remove any residual nickel. The nickel recovery was 93% after the residual nickel was washed out of the solids residue.

The nickel could be recovered from the solution by raising the pH to a value of about 8.5, by the addition of lime or sodium hydroxide.

For comparison, the ore was also treated with iron (III) sulphate solution at pH 1.0.and 50°C for 24 hours to extract nickel. Only 16% of the nickel was recovered in this process. These results are summari ed in Table 4.

Table 4 Nickel Recovery from Ore N 1 Treatment Nickel in Nickel Method Residue5 Extraction

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1 i (by weight) (by weight) Iron (III) 2.03% 16% Leaching Bacterial 0.60% 78% Oxidation Bacterial 0.19% 93% Oxidation Washing The results of this test showed that base metals in ore as sulphide minerals can be recovered by the action of the thermotolerant bacteria culture MTC 1. The sulphidic minerals were oxidised to release the nickel into the acidic solution for conventional recovery.

EXAMPLE 3 A gold bearing arsenopyrite pyrite concentrate was treated according to the present invention. This concentrate was designated AP 1. The major sulphide minerals were pyrite, 30% by weight and arsenopyrite, by weight. Other minerals present were calcite, quartz and chlorite. The gold was present almost completely in the arsenopyrite.

The concentrate had the following assay.

Table Assay of Arsenopyrite Concentrate AP 1 Element Symbol Assay (by weight) Gold Au 80 ppm Arsenic As 16.7 Iron Fe 28.1% Sulphur s 30.0% Al ICv i WO 92/16667 PCT/AU92/00117 10 Nickel Ni Samples of the concentrate were mixed with a sulphuric acid solution at a pulp density of 3% w/w to provide a pH range of 1.0 to 1.3. Nutrients included in the acid solution were ammonium sulphate at 200 mg/L, di-potassium hydrogen phosphate at 400 mg/L and mnignesium sulphate heptahydrate at 400 mg/L.

The acid level (pH) may vary from the start value and may either rise and then fall or fall from the outset. In most tests, the variation can be significant with the final pH often less than The slurry was inoculated with the thermotolerant bacteria culture designated MTC 1. The inoculate slurry was shaken in conical flasks at a temperature of 40°C. Samples were removed periodically and analysed for iron and arsenic extraction to determine the progress of the treatment.

The sample was treated by bacterial oxidation for 12 days to achieve 90% break down of the arsenopyrite mineral. The solids weight loss due to the oxidation process was The residual solids were then separated from the acid solution. Leaching of the separated solid residue using alkaline cyanide solution recovered 95% of the gold. In comparison, cyanide leaching could recover only 21% of the gold from the concentrate in the untreated state. These results are summarised in Table 6.

Table 6 Gold Recovery from Untreated and Oxidised Concentrate Sample -Arsenic Gold Recovered Extracted by Cyanide i WO 92/16667 PCT/AU92/00117 11 (by weight) Leacaing (by weight) Untreated 0% 21 Bacterial Oxidation 90% The cyanide solution employed to recover the gold contained sodium cyanide at a concentration of 2 g/L.

The arsenic and iron in the solution from the bacterial oxidation process can be removed by adjusting the pH to above 5.0 by the addition of lime, limestone, alkaline tailings or sodium hydroxide.

The results of this test show that gold encapsulated with arsenopyrite (FeAsS) can be released from the sulphide lattice by at least partial oxidation of the arsenic, sulphur and iron by the thermotolerant bacteria culture MTC 1 to render the gold accessible to cyanide solution.

EXAMPLE 4 A gold bearing arsenopyrite pyrite concentrate was treated according to the present invention. This concentrate was designated AP 2. The major sulphide minerals were pyrite, 90% by weight and arsenopyrite 9% by weight. Other minerals present were calcite, quartz and chlorite. The gold was distributed in both the arsenopyrite and the pyrite.

The concentrate had the following assay.

Table 7 Assay of Arsenopyrite Pyrite Concentrate AP 2 Element Symbol Assay (by weight) Gold Au 54 ppm Arsenic As 4.2% it \>i 1 J UI re .35.7% Sulphur S 40.0% Samples of the concentrate were mixed with a sulphuric acid solution at a pulp density of 10% w/w to provide a pH range of 1.0 to 1.3. Nutrients included in the acid solution were ammonium sulphate at 200 mg/L, di-potassium hydrogen phosphate at 400 mg/L and magnesium sulphate heptahydrate at 400 mg/L.

The acid level (pH) may vary from the start value and may either rise and then fall or fall from the outset. In most tests, the variation can be significant with the final pH often less than The slurry was inoculated with the thermotolerant bacteria culture designated MTC 1. The inoculated slurry was shaken in conical flasks at a temperature of 53 0 C. Samples were removed periodically and analysed for iron and arsenic extraction to determine the progress of the treatment.

The sample was treated by bacterial oxidation for 12 days to achieve 90% oxidation of the arsenopyrite mineral and an additional 21 days for 70% pyrite oxidation as well as arsenopyrite oxidation. The weight loss due to the oxidation process was 25% for the arsenopyrite and 78% for the 100% arsenopyrite plus 70% pyrite. The solids residue was then separated from the acid solution.

Leaching of the solid residue using alkaline cyanide solution recovered 79% of gold for the oxidation of arsenopyrite and 87% for complete oxidation of the arsenopyrite and 70% of the pyrite. In comparison, cyanide leaching could recover only 53% of the gold from the

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1 ii j _1I i~ WO 92/16667 PCT/AU92/00117 13 concentrate in the untreated state. These results are summarised in Table 8.

Table 8 Gold Recovery from Untreated and Oxidised Concentrate Sample Recovered Arsenic Iron Gold weight) Extracted (by weight) Extracted (by weight) Untreated 0% 0% 53% Bacterial Oxidation 90% 79% Bacterial Oxidation 100% 87% The cyanide solution employed to recover the gold contained sodium cyanide at a concentration of 2 g/L.

The arsenic and iron in the solution from the bacterial oxidation process can be removed by adjusting the pH to above 5.0 by the addition of lime, limestone, alkaline tailings or sodium hydroxide.

The results of this test show that gold encapsulated with arsenopyrite (FeAsS) and in pyrite (FeS2) can be released from the sulphide lattice by at least partial oxidation of the arsenic, sulphur and iron by the thermotolerant bacteria culture MTC 1 to render the gold accessible to cyanide solution. This example also shows that the MTC 1 culture is able to operate according to the invention at 53 0

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WO 92/16667 PC/AU92/00117 14 The thermotolerant bacteria culture MTC 1 was isolated from a coal mine in Western Australia. Sludge and water samples were taken and used to inoculate volumes of a modified 9K medium containing yeast extract. The samples were incubated at 30*C, growth was observed after 7 days. These samples were then sub cultured in modified 9K medium without yeast extract.

Modifications and variations such as would be apparent to a skilled addressee are deemed within the scope of the present invention.

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Claims (5)

1. 2. A process according to claim 1, characterised in that 16 the aqueous solution is acidic. 17 3. A process according to claim 2, characterised in that 18 the aqueous solution has a pH in the range from 0.5 to 19 4. A process according to any one of claims 1 to 3, characterised in that the thermotolerant bacteria is 21 acidophilic. 22 5. A process according to any one of the preceding claims, 23 characterised in that the thermotolerant bacteria is 24 aerobic.
2. 6. A process according to claim 5, characterised in that 26 the aqueous liquid is aerated during the operation(,of the 27 'process. 28 7. A process according to any one of the preceding claims, 29 characterised in that the thermotolerant bacteria is 0 capable of autotrophic growth. i I PF-.A/SUfiB-iTUT I SHEET ^Jk_ -16-
3. 8. A process according'to any one of the preceding claims, characterised in that no CO 2 is supplied to the thermotolerant bacteria during the operation of the process other than that available from ambient air.
4. 9. A process according to any one of the preceding claims, characterised in that the aqueous liquid contains sodium chloride in an amount up to 20 grams per litre. A process for recovering metals from particulate refractory precious or base metal containing sulphide material substantially as hereinbefore described with reference to any one of examples 1 to 4., i i 4 INTERNATIONAL SEARCH REPORT 1.CLASSIFICATION OF SUB3JECT MATTEtR of soerall 4iaelloolen uyw** sapply. kiloate slug According to International Patent clasalficstion IWO at to both Natlot Clausiicaion and IPC Int. Ci.' C228 3/18, C1 2S 13/00 C220 11/O0,.23/00(CI 2S 13/00, Cl2R 1:01)
5. 11. FIELDS SEARCHED Minimum Documentation Searched 7 Classification Sstem clasuiflloat" Swpobols It. C1. 5 C225 3118 Int. C1. 4 Cl 18 3/00. 11/04, 23/04 to thhare c AU IPC as above Ill. DOCUMENTS CONSIDERED TO BE RELEVANT' Category* Citation of Doounront, with Indicatimn whale appropriate of the reloent pasaog. 12 Relovent to Claim Nao PX Chemical Abstracts, Volume 115, No. 24, issued 199 1, 16 December (1-9) (Columbus, Ohio, P.A. Spencer, J.R. Budden, and M.K. Rhodes, "Bacterial Oxidation an scanimnic alteraritive for the teatment of refactmiy gold concentrates-, see page 261, column 1, abstract no. 260300n Australas. Inst. Min. MetaU. Pubi. Ser. 1991. World Gold 59-64 (Enal. X US,A,4729788 (HUTCHINS 9t 21.) 8 March 1988 (08.03.88) (1-91 See the abstract; the claims; column 3, lines 6-23. X US,A,4822413 (P0OLEY at al.) 18 April 1989 (18.04.89) (1-9) Se column 8, lines5 31-33. (continued) Special categories of cited documients i Later document published aft"i the International filing date or priority date and not In conflict Document defining the general &tat* of the art whiah to witht the opploodon but cited to understand the not coneidered to be of pidaular relevance principle or theory underlyna the invention -IE earlier documar-t but pubiad on or after the W document of particular relevance; the claimed4 intornationall fling dote invention canrot be considered novel or cannot be -L document which may throw doubts on priority alaimnis) considered to Involve en Inventive step or which i cited to establish the paibcotlon date ef Y4 document of particular reloence; the ulaimed another citation or other special reason (as spacified) Invention cannot be considered to Involve an doaunent reforring to an o~ral disclosure, use, inventivo stop when the document is combined exhibition or other inns with one or more other much documenta. such .P document published prior t the international filing dties comb~ination being obvious to a person skilled in but later then the priority date claimed the atof. documnent mnember o h io aetfrA IV. 'k'CERTIFICATION Date of the Actual Completion of the Internotional Seairch Date of Melling of tis International Search Report 22 June 1992 (22.06.921 30 June 1992 (30.08.921 international Searching Authority Signatre of Autherlid Ofter AUSTRALIAN PATENT OFFICE V. THOM FURTHER x x (I .4. IntsmuaoW Applation No. PCTZAU !~2;001'rl INFORMATION CONTINUEDFRO THE SECOND SHEET Y US,A4752332 IWU et al.) 21 June 1988 (21.05.88). See column 7, lines 7-24. US,A,4740243 (ICREBS-YUIU. at al.) 26 April 1988 (28.04.88). See column 7, linc 44-61. CAPA 122414 (INTEROX CHEMICALS) 27 April 1952 (27.04.82). Sea claims I and 7. AU.A.52258/90 (GENERAL MINING METALS AND MINERALS) 3 Octobet 1991 (03. 10.9 See claim 3. USA,5030426 (BOWERS-IRONS at al.) 9 July 199 1 109.07.911. See column 2, lines 21-34; column 4, lines 4-7. (1-9) (1-9) (1-9) (1-9) (1-9) V. OBSERVATIONS WHERE CERTAIN CLAIMS WERE FOUND UNSEARCHABLE' Thslnternationa search report has not been eatablished in resPect Of certain claimsa Under Article 17(21s) for the following reasons: i:.h 0 Claim numbers..., becase. they relate to subject matter not required to be sarchod by this Authority. namely. 2. Clefrim bes...,Iem e ohtrlt op~wf$h nentoa n thaon o cmywith the prescribed Ie~emnbto suon an extor tt no meaningiu mternatind xesr coano a arned out, epee icl y: 3. Clai nunib r. *~el hey ore, depend-nt claims and are not drafted In accordance with tha second and third VI. I] OBSERVATIONS WHERE UNITY OF INVENTION IS LACKING2 This lnisrnedonal Searolting Authority found multiple inventions in this internatlonao pploatlon en follows: l~dj~di~d n erna lot v I oil adby the applioant, this International search report covers Aomtl r f the.Y cequlrd nd~tionall f poer Li~ m fldb the o o t search report ove y to sfe; the Waernetd wloato orMTVie 3. 1JNogy9 ided adiyonVAI eearh teesr~~ero tlm WvpJdby t4s alicant acrl ~un tiy. tinte'national scarch report is the rnena rt mentoe mntcam; nt n cOvere b im Num Zs 4. dA at uparchoble claims pould be v~h~d without effort jusflVmN; an additional toe, the Internotional Searching Authority no mopaymnent or any additc so. Remark on Petest Thu additional search fees were eacomnpanod by applIcant's protust. QNo protest acocnpiorded the payment of adtonal march foes. i. of I tr 1 Nutrients included in the acid i solution I 4 I 'V mn~ ANNEX TO THE INTERNATIONAL SEARCH REPORT ON INTERNATIONAL APPLICATION NO. PCT/AU 92/00117 This Annex lists the known publication level patent family members relating to the patent documents cited in the above-mentioned international search report. The Australian Patent Office is in no way liable for these particulars which are merely given for the purpose of information. Patent Document Cited in Search Patent Family Member Report US 4729788 AU 10328/88 ZA 8800071 US 4822413 AU 69934/87 CA 1292623 ZA 8701399 ZW 38/87 US 4752332 AU 62936/86 US 4740243) US 5030426 AU 60378/90 US 5030425 WO 91/00369 END OF ANNEX I 1