EXPERIMENTS ON COMBINED ELECTRO AND BACTERIAL LEACHING (Short Communication)

EXPERIMENTS ON COMBINED ELECTRO AND BACTERIAL LEACHING (Sho Communica ion) K.P. Teppe and R. Na eke Leh s uhl ii Mik obiologie, Technische Uni e si a B aunschweig B aunschweig, FRG Abs ac : The in luence o di ec cu en and o cu en wi h changing he poles wo imes pe sec a in ensi ies o 0,2...15 mA and a ensions o 12...170 Von leaching o py i e dispe sed in qua zi e in pe cola- o s wi h Thiobacillus e ooxidans was s udied. The solu ion o i on was accele a ed by bac e ia wi hou cu en and by cu en wi hou bac- e ia, bu in combina ion he accele a ion did no exceed he sum o bo h single e ec s. The esul s sugges ha he e is no di ec elec- ophysiological in luence o cu en on bac e ia unde condi ions o ou expe imen s. A p esen we y o u ilize indi ec elec ochemical e ec s o cu en on bac e ial leaching o chalcopy i e. In oduc ion We epo abou ou i s expe imen s which we e s a ed o ge answe s on some ques ions ela ed o a combina ion o elec oleaching wi h bac e ial leaching o o es. Do hese p ocesses in luence each o he o one ano he so ha he e ec is g ea e o smalle han he sum o he e ec s o he single p ocesses? Is he e any di ec elec ophysio- logical in luence o elec ic ield o cu en on he bac e ia, o is he e me ely an indi ec e ec , e.g. by elec ochemical p ocesses in he medium s imula ing o inhibi ing he g ow h? May bac e ial me abo- lism accele a e (o inhibi ) he elec oleaching? To look o mo e di ec elec ophysiological in luences in he i s se o expe imen s we ha e chosen py i e as he mine al o be leached o i is‘known ha wi h low cu en in ensi ies he e is no o ma ion o elemen al sul u om py i e which would se e as ene gy sou ce o Th obaeilli. [ne o ma ion o S° would ep esen an indi ec elec ochemical e ec . 212 K. P. Teppe and R. N&é eke Me hods We used pe cola o s as shown in ig. 1. The medium, 230 ml 9 K medium o Sil e man and Lundg en /1/ wi hou e ous sul a e, was mo ed h ough he pe cola o by ai li . The calumn was illed wi h a mix u e o acid washed qua zi e (diame e o he pieces 5...10 mm) and 200 g py i e (diame e 0,5...2,0 mm). A 1 cm? pla inum shee was inse ed as elec ode in he uppe laye o he subs a e. The o he elec ode - o he same shape - was inse ed in he bo om pa benea h a pe o a ed e lon shee . This pa was illed wi h medium up o he qua zi e. Vol age and cu en we e deli e ed by an equipmen by which a cons an cu en in ensi y o 3, 8, 9, 12 o 15 mA (p o ided ha he aol ace o Up. o 230.) was. su i- cien ) o a cons an ol age up o 230 V (p o ided ha he cu en in- ensi y did no exceed 15 mA) was kep cons an . I on concen a ion was de e mined by AAS, bac e ia concen a ion by di ec mic oscopic coun ing. UPPER ELECTRODE < QUARTZITE a + PYRITE } oe AIR LIFT PERFORATED TEFLON SHEET 9K MEDIUM w R LOWER ELECTRODE H SCREW TUBE CLAMP Fig. 1: Pe cola o o combina ion o bac e ial and elec o leaching o py i e wi h Thiobacillus e ooxidans Combined Elec o and Bac e ial Leaching Expe imen s wi h 9 mA 213 In mos expe imen s we wo ked wi h di ec cu en o an in ensi y o 9 mA, he uppe elec ode as anode, s a ing a he beginning o a he second day o he expe imen . In some expe imen s we in e up ed he cu en e e y 5 sec o 5 sec, and in some o he expe imen s we he poles wo imes pe sec. A he beginning he concen a ion e ia was 2.<.14,5 x 107 ma and he pH was 3,0...3,2. Con ols up wi hou elec ic cu en , wi hou bac e ia and wi hou bo h. 7? days un a 26°C in. he da k we ion in he medium. was measu ed and added o ha o sul s o some expe imen s o his a e shown in able 1. : o The amoun o Fe changed o bac- we e se A e measu ed pH and o al i on concen a- p ecipi a ed on he elec odes he o al i on in he medium. The en g oup wi h cu en in ensi y o 9 mA 0 6 o al i on leached om py i e and pH 3 mA e e a e 7 days a 28°C in he da k cu en Be ne ao = 0 | bac- Fe| pH Fe| pH Fe| pH Fe| pH days | low Ge os e ial) mg, mg | mg, mg, o 0 0 112,78 112,60 1|2,90 112,778 113,15 oO o + 193 11,80 214 1,90 S50 (75 | 31911575 47614,821 212 11,90) 345 11,71 | 299)1,80 4.77 +| CONLIN «| o = o (112525 30 12,25 PANN20 7 2.-7.{con in.| + - a 24 2,20| 5012.20 412,21 1.-7.{in e .| + - 0 38 |2,20 13512;29 4.7-7. con in. + = + 235 1,60) (00 11,95 9511,94] 269 11,80 45 12,00 63 ;2,00 972,01 2.57. COn in«l + = + 4621165 | 160 11,90 35631,70 156 /1,90 344-14 5.75 Ao 7 an ennal = j 3241 11,75 7] 31214,80 | 354 11,721 169 11,96 | 1.-7.| con in.|changing + i S541, 70 4 { i Table 1: Resul s o ou se ies o expe imen s on py i e leaching wi h Thiobacillus e ooxidans in combina ion wi h elec ic cu en o 9 mA in ensi y. in pe cola o s 214 K. P. Teppe and R. Naé eke The esul s show clea ly ha wi hou bac e ia and wi hou cu en he e is p ac ically no solu ion o i on, wi h cu en alone wi hou bac e ia he leaching is only slowly. In expe imen s wi h bac e ia one can no see an accele a ion o bac e ial leaching by cu en . I mus be concluded om he g ea di e ences be ween he alues o pa allel esp. simila expe imen s, ha he e mus be some unknown ac o s which in luence he bac e ial leaching p ocess. Bu looking a all da a i can be concluded, ha i is unlikely ha he e a e di ec posi i e physio- logical e ec s o he cu en on he bac e ia, a leas unde he con- di ions o ou expe imen s. Expe imen s wi h 0,2 and 1,0 mA We had o ake in o accoun he possibili y ha a posi i e in luence o he cu en on he bac e ia was abolished by nega i e in luences o elec ochemical e ec s. So we s a ed ano he se ies o expe imen s o simila ype as desc ibed abo e bu wi h cu en in ensi ies o only 1,0 and 0,2 mA and o e a pe iod o 30 days. Du ing his ime we measu - ed e e y day pH, o al i on concen a ion and concen a ion o bac e ia in he medium. Wi hou bac e ia he e was almos no change a all in pH and no i on was dissol ed. Wi h bac e ia he e was a dec ease o pH and a change in i on concen a ion wi h wo maxima as i is seen in ig. 2. This shape o he cu e was he same in se e al expe imen s, each wi h se e al pa s allels. The concen a ion o bac e ia dec eased in all expe imen s in he i s 3 days by abou 10°, possibly by adhesion on o he su aces o he solid; hen i inc eased o 4 alue sligh abo e ha a he be- ginning and hen emained cons an . I is seen in ig. 2 ep esen ing ypical esul s o an expe imen wi h 1,0 mA ha he e is p ac ically no di e ence be ween pe cola o s wi h cu en and wi hou . This was he case as well wi h cu en in ensi y o 0,2 mA as wi h 1,0 mA. Conclusion I can be concluded om ou esul s ha - a leas in ou expe i- men s - he e is no di ec physiological in luence o cu en on he bac e ia. An enhancemen o bac e ial leaching by low cu en in ensi y epo ed by o he au ho s, e.g. /2/, mus depend on indi ec elec oche- mical e ec s. Bu ob iously hese e ec s we e absen in ou expe imen s wi h py i e. Combined Elec o and Bac e ial Leaching 215 10+ ‘ 8a a m on [ 6 Oo = SN—WITH CURRENT Oo Se M9 SWITHOUT CURRENT Pp” oO os ~~ 2- 0-4 10°+ ou _-WITHOUT CURRENT xb “WITH CURRENT , 19/4 << ye, ' io 10°4 /! oo we © {| < x mM 10-4 3,07 T 20+ _MWITHOUT CURRENT 10 : , —-WITH CURRENT 6 10 20 30 TIME [DAYS] Fig. 2: Leaching o py i e wi h Thiobacillus e ooxidans in pe cola- o s a 26°C, da k meme Wi h di ec cu en a cons an in ensi y o 1,0 mA meme wi hou cu en 216 K. P. Teppe and R. Na eke Ou look F om epo s o Ralph /3/ and o 1114 and Be am /4/ i mus be con- cluded ha a leas in he case o chalcopy i e one can expec posi i- e in luences o cu en on bac e ial leaching. By anodic oxida ion ele- men al sul u is o med on he su ace o chalcopy i e c ys als so ha an easily u ilizable ene gy sou ce o Thiobacilli, especially o T. hiooxidans, is deli e ed. This migh be seen as an enhancemen o elec- o leaching by bac e ia a he han an enhancemen o bac e ial leaching by cu en : The o ma ion o elemen al sul u dec eases he cu en in- ensi y by insula ion he chalcopy i e pieces by a laye o sul u on he su aces and he e o e inhibi : he leaching p ocess. Thiobacilli oxidize his sul u and hus keep he su aces clean and mo eo e o m sul u ic acid, which i sel accele a es he leaching. We will ollow his line o esea ch. Re e ences /1/- M.P.Sil e man and D.G.Lundg en, J. Bac e iol. by B42 (1 959)) /2/ §.8.Gajda zie and F.N.Gence , Chimija i Indus i a, So ija, 44. 18 (1972) cn 73/7 -B.9:Ralph, his monog aph /4/ H.1I11i and R.Be am, his monog aph