S. Acar and P. Somasundaran

Abstract - The re8Ult8 obtained for ~ 8electfveflocculation of natural ore8 do not uaually agree withthe corre8ponding propertie8 of the comtituentmfneral8 when pre8ent alone. Thfa fa mainly due to thepre8ence of dwolved mineral apecie8 which caninteract in many UXlY8 wUh other comp0nent8 in ~81J8tem and alter their behavior. In thfa paper, theeffect of di88olved apecie8 on the flocculation andelectrokinetic propertie8 of 8ul/ide mineral8 fa dfa.cuaaed. Di88olved iron, copper, and nickel (Fe, Gu,and Ni) apecie8 are found to affect the propertfe8 ofnatural chalcopyrite and pentlandite in certain pHrange. These effect.. are interpreted in teTm8 ofapecie8 adaof'J)tion leading to activation or depre88ionof reagent.., aurface precipitation, and comple~tionof8pecie8.

Polymer: Polyethylene oxide polymer was obtainedfrom the Union Carbide Co. Molecular weight of thesample was found to be 5.105.

Inorganic reagents: Fisher certified HCI and NaOH(IN, O.lN, and O.OlN) were used to adjust the pH of thesuspensions. Amend Drug and Chemical Co. reagentgrade NaCI, which is 99.96% pure, was used to prepare3.10 -2 kmol/m a salt solution for all the experiments.

Water: Triple distilled water with specific conduc-tivity of about 10 -8 lIJnhos/cm, made using a quartzstill, was used to prepare all the solutions.

Methods

Introduction

Flocculation: For nocculation purposes, 8 g (0.2 oz)samples of a -20 IJ.m (-825 mesh) mineral samplewere equilibrated for three hours in 3.10 -2 kmol/m'NaCI solution at the desired pH in 250 cms (15 cu in.)tenon bottles on a wrist action shaker. Flocculationtests were conducted in 250 cms (lG cu in.) beakers(with specially designed baffies) at 3% weight pulpdensity. In the case of tests involving polymers, thedesired amount was added to the pulp and furtherconditioned for three minutes by stirring with a2fi mm diam (1 in. diam) propeller at 12OOrpm.

The mineral was then allowed to settle under gravityfor 15 seconds. The top GO% of the suspension waswithdrawn using a specially designed suction device.The pH of the pulp was monitored at the end of eachtest. The two portions were then filtered, dried, andweighed. The percentage of excess solids settling in lGseconds was taken as a measure of the nocculation ofthe minerals. Analysis of the dried residue was con-ducted in the case of selective nocculation tests ofm1xtw'es.

Electrokinetic studies: Electrophoretic mobl11ty ofminerals conditioned as desired were measured usinga Zeta-Meter in mineral supernatants and in selectedinorganic electrolytes under given experim~ntal con-ditions. A ~ ppm suspension of mtneralis preparedand equilibrated for a given condition before themeasurements are done in a plexiglass cell.

Preparation 01 mitaeral supernatants: A mineralsample was conditioned for three hours in S.10-2kmol/ms NaCI solution at room temperature and atdesired pH in 250 cm3 (lG cu in.) tenon bottles on awrist action shaker. The suspension was then filteredthrough pretreated - by washing several times withthe same supernatant - No. 44 whatman fnter paper.The supernatant was stored in tenon bottles for nomore than one week.

The efficiency of mineral processing techniques,particularly selective flocculation, depends mosUy onthe surface chemical properUes of the constituentminerals. Ionic species present in the system, either inthe form of impurities introduced through the waterand the reagents used or the dissolution of theminerals, can alter the surface chemical properties ofthe minerals s1gn1f1canUy (Ananthapadmanabhan andSomasundaran, 1984; Attla, 1977; Critchley and Jewitt,1979; Drzymala and Fuerstenau, 1981; Heerema, Llpp,and Iwasaki, 1979; Heerema and Iwaaakl, 1980;Klrshnan, 1984; and Somasundaran, 1978). It has beenreported by severalinvest1gators that the presence ofspec1f1cally adsorbing ions such as 012+, Ca2+, Mg2+,and Fes+ can change the zeta potential of quartz,resulting in activation or deactivation of It in floccula-tion. Heerema reported that the presence of Ca2+and Mg2+ ions in the suspension of Iron ores resultsin the nonselective flocculation of Iron oxide and thesll1cious gangue (Heerema, Llpp, and Iwasaki, 1979;Heerema and Iwasaki, 1980). It is clear that the effectof dissolved species on the efficiency of the abovebeneficiation process can be critical espec1ally whensparingly soluble minerals are present together.

In this study, the effect of the dissolved species ofchalcopyrite and pentiandite on the flocculation ofthese minerals has been investigated by conductingtests in the presence of supernatants of each other.

Experimental materials and methods

Materials

Minerol8: Natural chalcopyrite was purchased fromWard's Natural Science Establishment Inc" andnatural pentlandite was obtained from InternationalNickel Co. Surface areas of -20 lAm (-625 mesh)particles of chalcopyrite and pentlandite, as measuredby the BET nitrogen gas adsorption method, were 1.22and 1.48m2/g (13 and 15 sq ftper 0.03 oz), respectively,Minerals were stored in tenon bottles and kept undernitrogen atmosphere,

S. Acar and P. Soma8undaf8n, members SME, are graduatestudent and professor, respectively, in the School of Engineer-ing and Applied Sciences, Columbia University, New York, NY.SME preprlnt 85-125, SME-AIME Annual Meeting, New York,NY, February 1985. MMP paper 65-612. Manuscript February1985. Discussion of this paper must be submitted, In duplicate,prlortoJan.31,1986.

MINERALS AND METALLUAGM:AL PAOCE8..0 NOVEMBER 1- .231

100PENTLANDITE03 x 10-2kmol/m3 NaCI6, CHALCOPY RITE SUPER.

are measured using a zeta-meter in 3.10-2 kmol/m3NaCI salt solution and in supernatants.

The zeta potential of as received chalcopyrite in saltsolution and in pentiandite supernatant are plotted asa function of pH in Fig. 9. The as received mineral wasobserved to have an isoelectric point (iep) of aboutpH 2. Above pH 2, it is increasingly negativelycharged. However, in the presence of pentlanditesupernatant, the negative surface charge is reducedsignificantly throughout the pH range studied.

800'"-J.-.-'"(/)

(/)0

-J0(/)

~

60

40 8&--6" O'_~";'--o-~

20

20O' I I I I I

2 4 6 8 10 12 14

pH

Fig. 8 - Pentlandite flocculation as a function of pH inchalcopyrite supernatant 0

>e

-..~.-Ztal.- - 200a..

~.-talN

-40

Dissolution and precipitatlon/readsorption of mineralspecies in mixed mineral systems is considered to be amajor reason for the observed effects. This wasfurther confirmed by electron spectroscopy for chem-ical analysis (Acar, 1985) and by electrophoteticmobility results. Esca spectrom of chalcopyrite con-ditioned in pentlandite supernatant and washed free ofthe supernatant showed that nickel ions can be foundon the surface of chalcopyrite. Similarly, the spectromof pentlandite conditioned in chalcopyrite supernatantand washed also showed presence of copper on thepentlandite surface.

The extent of the dissolved species in the chalco-pyrite and pentlandite supernatants at different pHvalues was determined using direct coupling plasma(DCP). The results are given in Tables 1 and 2. 2 .. 6 8

pH

10 12 14

Table 1 Chemical Analysis of Chalcopyrite Supernatant Fig. 9 - Zeta potential of chalcopyrite in NaCI and pentlanditesupernatant solutionspH ppm CuT

10352nilnil0.30.2

ppm FeT501431

nil0.010.30.1

4.3 (natural)79

1112.4

Table 2 - Chemical Analysis of Pentlandite Supernatant

P"3..1 (natural)79

11tab

ppm NIT2311~193

nilnil

ppm ,.T~20.30.8nilnil

Figure 10 shows zeta potential of pentlandite as afunction of pH with isoelectric points at pH 8 and pH 10.The latter iep is possibly the result of the formation ofNiO (iep: 10.3) and Ni(OH)2 (iep: 11). On the otherhand, the lower iep can also be due to the formation ofoxides {FeO (iep: 8.2-6.7), FaO. (iep: 6.5), and Fe20S(iep: 6.7 -8.2)} and hydroxide {FeOOH (iep: 7)} on thepentIandite surface (Parks, 1965).

As in the case of chalcopyrite-pentlandite super-natant, the zeta potential of pentlandite was ~reduced considerably by the chalcopyrite supernatantthroughout the pH range studied. This was due to theadsorption or surface precipitation of the dissolvedchalcopyrite species on the pentIandite surface.Remember that the flocculation of these minerals wasalso similarly affected by the supernatant of eachother. To identify the species actually responsible,zeta potential measurements of synthetic sulfideminerals were also conducted in inorganic solutionscontaining each species. The results, discussed else-where, showed Cu, Ni, and Fe species to affect thesurfaces of the various minerals to different extents(A car and Somasundaran) .

t

The above analysis results show that the amount ofdissolved species is significant enough under certainpH conditions to have an effect on the flocculation.

Electrokinetic studies

Electrokinetic studies help develop an understand-ing of the processes occurring at the solid-liquidinterface under different conditions. Therefore, elec-trophoretic mobility of chalcopyrite and pentlandite

MINERALG AND METALLURGICAL PROCESSING234 NOVEUeER1985

in the complete pH range studied. In the presence ofsupernatants, zeta potentials of chalcopyrite andpenUandite are found to be reduced considerably dueto the adsorption or surface precipitation of dissolvedions and their hydroxy species on the mineralsurfaces. .Acknowledgments

The authors acknowledge the National ScienceFoundation (CPE.SS-18163, CPE-83-04059), INCO Inc.,and Union Carbide Corp. for support of this work.

References

pH

Fig. 10 - Zeta potential of pentlandite in NaCI and chalco-

pyrite supernatant solutions

Summary

Results of single mineral flocculation tests showedthat polyethylene oxide is an efficient flocculant forchalcopyrite. This is probably due to the partialhydrophobicity of the mineral and the polymer.Pentlandite, on the other hand, is not flocculated byPEO. When both minerals are present in the suspen-sion in equal amounts, selective flocculation of neithermineral could be obtained. This is mainly due to theeffect of dissolved mineral species either throughadsorption or surface precipitation.

These considerations were supported by the floccu-lation and electrophoretic studies conducted in thepresence of supernatants. Flocculation results showedthat chalcopyrite was dispersed by the pentlanditesupernatant in the acid pH range while pentlanditeflocculation was activated in chalcopyrtte supernatant

Acar, S., and Somasundaran, P., "Effect of dl88olv8d miner" species on the atepotentlel of sulfides," to be published.

Acar, S~ 1~, "Interactions between polymer, complexlng reeoent and dissolvedmlnef81 species In selective flocculation tyStems," DESc di8Hrtatlon, ColumbiaUn'-8lty, Henry Krumb School of Mines, N- York.

Ansnthapadman8bhan, K.P., and Soma8und8r8n, P., 1984, "Role of dluolvedmlnefal species In calclte-apatlte flotation," Mineta/8 .m AfetellUtpical Process-Ing, May, pp. 38-42.AUla, Y.A.I., 1977, "Development of a selective flocculation PfO':888 for a complexcopper ore," In/8mat/ona1 Journal of MineraI P_alng, No.4, pp. 2(»-225.Critchley, J.K., 8M J_Itt, S.R., 1979, "TIle effect of CIA2+ Ions on zeta potentl81of quartz," T/8na. Institution of MinIng and Metallurgy, (Sect C: Minerai Proc-.Extr. Metall.) 88, C57 - 59.

Critchley, J.K., and Straker, P., 1.1, "Flotation of hlc«el sulphide and zetepotentials In nickel (2) - xanthate sy.tern," T/8na. InstItution of Mining andMetallurgy (Sect. C: Mlnef8I proce... Extr. Metall.),~, pp. 44-45.Orzymala, J., and Fueratenau, O.W., 1.1, "Selective flocculation of hematite Inthe hematit.quattz-ferrlc ion-polyacrylic acid system. Part 1, activation anddeactivation of quartz," International Journal of Mineral Procesa/ng, No.8,pp.265-277.

Fuerstenau, M.C., and Sabecky, 8.J., 1.1, "On the halural flotability of sulfides,"International Journal of MIneraI PItlCeSSlng, No.8, pp. 79-84.Heerema, R.H., Upp, R.J., and Iwasaki, I., 1979, "Complexation of calcium Ion Inselective flocculallon of Iron ore," SME.AIME Annual Meeting, N- Orleans, LA,Feb. 21.

Heerema, R.H., and Iwasaki, I., 1980, "Chemical precipitation of aI~lne earthcations and its effect on flocculation and flotation of quartz," T/8ns. SME-AIME.Vol, 288, pp. 1510.1518.Kirshnan, S. V., 1984, "Influence of surface preclpitetlon on separatIon processes,"15th Annu81 Meeting of the Fine Particle Society, July ~-Aug. 1, Orlando, FL.

Partca, G.A., 1~, "The I8oelectrlc points of oxides, solid hydroxides, and aqueoushydroxocompiex systems," ~mical Review, No. 85, p. 177.Rubio, J., and Kltchener, J.A.. 1978, "The mechanism of 8daorptlon of polyethyleneoxide flocculant on slllca," Journal of Colloid SM Inl8rface Science, No. 57,pp.132.142.Rubio, J., 1.1, "The flocculation properties of poIy(ethyleneoxlde)," Colloids andSurfaces, No.3, pp. 79.95.Soma8undaran, P., 1978, "Selective flocculation of fines," presented at sym.poslum on "The pilyslcal chemistry of mlneraJ.reagent Interactions In sulfideflotation." College Park, April 8- 7.Trahar, W.J., and Viarren, U., 1976, "The flotability of very fine particles - Arevl_," International Journal of Mln.,.' Processing, No.3, pp. 103-131.Union Carbide Corp., "PoIyox," FIOCCUlAnts Trade Information.

MIHiMLS .-.NO METALLURGICAL PRooe8$HO NOVEM8ER 1985 23S

S.E. Clay

Abstract - In the chemical reaction control regimeemployed in the laboratory dissolution experiments,calcined trona ore dissolves in aqueous solutionsaccording to a first order, irreversible reaction rate.The study showed that the reaction is first order withrespect to solution NasCO" concentration. The activa"tion energy was determined to be BO. S33 kJ / g . mol witha rate constant equal to 1835 mm/s (1917 in. per min).The dissolving particle may be described by shrinkingparticle behavior.

Introduction

Soda ash (Na2COS) is typically produced from thenatural trona (Na2COS.NaHCOs.2H20) deposits ofthe Green River Formation in southwestern Wyomingby one of two processes. In one process, the trona isdissolved to obtain a solution containing Na2COS andNaHCOs. This solution is carbonated and crystallizedto NaHCOs, and is calcined to Na2COS. The othertypical process calcines the ore to crude Na2COS'which is then dissolved in aqueous solution, purified,crystallized to sodium carbonate monohydrate(Na2COS . H2O), and dried to soda ash product.

Some work has been done on raw trona dissolutionfor solution mining (Guilianelli et al., 1981; Saldickand Cohen, 1980), and on the use of additives to extractalkali values from ores (Frint, Copenhafer, andPinsky, 1979). Gancy (1979) discusses countercurrentcontacting of calcined trona and solution to affectNa2COS recovery and washing of the remaining ore.However, no studies of the dissolution rates have beenpublished. This paper presents the results of achemical kinetic study of calcined trona dissolutionin aqueous solutions.

using a tachometer. The solution was heated to thespecified initial temperature (Hg bulb measurement),as was the solid sample. The reference thermocouplewas placed in a constant temperature bath (necessaryto keep the thermocouple output within the range ofthe millivolt recorder) and the measuring thermo-couple was placed into the reactor solution. Therecorder was zeroed and set at a chart speed of 254mm/min (10 in. per mill). The entire calcined samplewas then transferred into the reactor and the tempera-ture rise of the solution was recorded on the millivoltrecorder. After the reaction was complete, therecorder chart speed was reduced to 254 mm/hr (10 in.per hour) and a final temperature was obtained usingan Hg bulb thermometer. The insoluble portion of theore was filtered out, washed, dried, and weighed.

Thermocouple output was calibrated at each reac-tion temperature using the average of three Hg bulbthermometer readings as the assumed actual tem-perature.

Initial reaction rates were used for all analyses asspecific conditions and system constants were allknown at the initial conditions.

Table 1 Insoluble Content of Calcined Ore Size Fractions

% Insoluble

7.414.954.922.973.023.343.924.045.235.94

Experimental descriptionMathematical description

The trona ore is first calcinedMaterials

The trona ore used in the experiments was hand-picked from Stauffer Chemical Co.'s Big Island Mine.The overall assay for the ore was about 95% sodiumsesquicarbonate (Na2COS .NaHCOs .2H2O). The orewas crushed and hand-screened to the requIred sizes.Each differed in assay, as indicated in Table 1. The orewas calcined at S50oC (662OF) for 16 hours before itsuse, thus assuring complete calcination. The dissolv-ing soiutions were made up of distilled water andStaufferLITE@ ash (99.6% Na2CO3 minimum).

-+ 3Na200I(8)

(1)

2Na2CX>. oNaHCX>a 02H20 (8)

CX>2 + 5H20((g) g)

and then dissolved

Na200a ( -.. Na200a (2)

s) (aq)

The particles of calcined ore shrink as they dissolveas shown by Table 2.Apparatus and procedure

The experimental system is shown schematically inFig. 1. One liter (0.26 gal) of solution was placed in thereactor and the stirrer was set to the specified rpm

Table 2 Dimensions of a Cubical Calcined Ore Particleas a Function of Dissolving Time

RHCtIon Time(sec)

051

1015

P.rtlcle Dlm.nslon (mm)x , Z

86 8.2 7.07.8 7.~ 6.S7.6 7.3 6.16.8 6.6 5.~5.8 5.3 ~.1

S.E. Clay is general manager of Taylor Metallurgical Laboratory,Moscow, 10. SME.MMP nonmeeting paper 85-631. ManuscriptApril 1985. Discussion of this paper must be submitted, Induplicate, prior to Jan. 31, 1986.

236 NOVEMBER 1985 MINERALS AND METALLURGICAL PROCESSING