quantitative analysis of gold concentrate using fire … · determination of gold following...

QUANTITATIVE ANALYSIS OFGOLD CONCENTRATE USING FIRE

ASSAY BY GRAVIMETRY ANDSPECTROPHOTOMETRY METHOD

Bayu Wiyantoko∗a, SantosobbProfessional Program of Chemical Analysis,

Islamic University of Indonesia*Corresponding author Email: *[email protected]

April 2, 2018

Abstract

The analysis of gold content in concentrate sample us-ing fire assay by gravimetric and sample basis cupel lossby Atomic Absorption Spectrophotometry (AAS) have beendone. Certification standard used was ISO 10378: 2005 -Cooper, Lead, and Zinc Sulphide Concentrates-Determinationof Gold and Silver-Fire Assay Gravimetric and Atomic Ab-sorption Spectrophotometry (AAS). The gold content ob-tained by gravimetric was 14.41 mg/g, and by spectropho-tometry was 0.12 mg/g. The results of both tests wereadded together in order to get the gold content that was14.53 mg/g in the ratio of standard concentrate that hasbeen certified which was 14.89 mg/g. The resulted of goldcontent by fire assay using gravimetric method based hada precision value (% RSD) was 3.3850%, while the valueof CV Horwitz was 10.7078%, and accuracy with truenessvalue of 99.06%. The AAS test results with precision of %RSD value was 41.1290% and the value of CV Horwitz was34.3292%. Meanwhile the accuracy test expressed the valueof % recovery around 99.88%, and for LOD and LOQ valuesrespectively were 0.6146 mg/L and 2, 0488 mg/L.

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International Journal of Pure and Applied MathematicsVolume 118 No. 24 2018ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

Key Words:Gold; Gravimetric; Atomic Absorption Spec-trophotometry; Fire Assay; Cupel Loss; Concentrate

1 Introduction

Gold is a chemical element in the periodic table that has the sym-bol Au (aurum) with an atomic number of 79, and gold includinga transition metal (trivalent and univalent) is shiny and yellow.Gold does not react with other chemicals and melt at temperatures1000◦C (1). Gold occurs in association with ores of lead, iron sul-fide, copper, in quartz veins in the gravel of stream beds. Goldhave four basic colors which are obtain by the use of two or morevaried quantities of base metals including silver, copper, zinc andnickel. Some precipitate formed because of metasomatism process,while mechanically concentrating produce sediment placer which isdivided into two categories namely primary sludge and sedimentplacer (2). Gold ore containing silver (10-15%), less copper, iron,metals Bi, Pb, Sn, Zn, and platinum in small quantities (2). Thegold is separated from other metal elements to obtain pure gold.In the geological samples, the concentration of gold is very low to-gether with the high concentration of matrix components that ofteninterferes the separation.

Gold separation and preconcentration contained in the geolog-ical samples have been developed using fire assay, coprecipitation,solvent and solid phase extraction besides possible used anotherways including amalgamation, sluice box, and cyanide leach. Theselection of suitable sample preparation is highly depends on thegold concentration and the further method to final determination.Basically there are three methods used for determining of gold likelygravimetry, titrimetry and instrumental. The last method for golddetermination including atomic absorption spectroscopy(3), neu-tron activation analysis (4) and inductively coupled plasma spec-troscopy (5). The gold separation in this research is done usingfire assay due to this is the most important method used for thepreconcentration of gold and for separation from their base met-als and silicates. The fire assay has known as classical method ofgold collection which currently used two kinds of collectors namelylead and nickel sulfide (6). The usage of the fire assay method was

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International Journal of Pure and Applied Mathematics Special Issue

performed for purification methods including gold content of thecheapest and most accurate to date compared to another methodeven the ability of this method can equal gold content testing usingX-ray machines. The fire assay using NiS collector has been usedfor quantitative recovery of gold from geological samples althoughmajor precautions to lower the level of contaminants from the fluxcomponents are necessary(7). The level of accuracy of the methodof separation by fire assay methods can achieve 0:04% (8). The finalresults of the analysis using fire assay method is then conducted theweighing of metal or measured with instrumentation such as atomicabsorption spectroscopy(8).

The analysis of gold grades in this research using two samplesare concentrates and cupel loss. The concentrate is the result ofthe concentrated of the ore containing high grade gold and silver,and determined using a gravimetric method. The cupel loss is acontainer that is used to process gold cupellation process, so whengold be merged on the cupel so the container named as cupel lossand analyzed using AAS. The determination of gold by fire assaymethod is necessary to acquire the precision, accuracy, LOD andLOQ values in order to figure out the measurements that have beendone has fulfilled the quality assurance of the test. The precisiondetermination was important to know whether the measurementbased on the proximity of the measurement results with measure-ment repeatability. The accuracy is the closest of the measurementresults with actual levels, so that the accuracy needs to be deter-mined to find out the accuracy of test results (9). Limit of detection(LOD) is the concentration or amount of the smallest / lowest ofthe analyte in the sample can be detected, and limit of quantita-tion (LOQ) is defined as the lowest analyte concentration in thesample can be determined with precision and accuracy that can beaccepted on the condition operational methods used (10). Basedon this background, the problem in this test includes quantitativeanalysis of gold content in the samples of concentrate and cupel lossusing fire assay by gravimetric and atomic absorption spectropho-tometry (AAS) as well as quality assurance testing results in termsof precision, accuracy, limit detection and the limit of quantitation.

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2 Literature Review

2.1 Concentrate

Concentrate is a product which is the result of concentration of theore/seed, in this case is meant copper containing approximately30% copper, but also contains high grade gold and silver. The goldcontent varies between 20 - 70 ppm, while silver is about 60 - 100ppm. Preparation of concentrate sample is drilling and blasting tobe obtained by ore, then crushed with the size of 75 um - 150 umand separation of Cu, Pb, Zn, Au, Ag, Pt, and Si by floating untilthe metal floats above and the precipitate is silica (tailings/waste).Concentrates sample that still contain lots of water is collectedand dried in the dewatering plan (DWP). The dried samples withmoisture content under 9% were loaded with bulk to the vessel, andsampling each time span and composed into one sample in each lot(± 2000 tons) (11).

2.2 Fire Assay

Fire assay is a quantitative method in analytical chemistry to de-termine the levels of precious metals such as gold, silver which aredetermined by extraction by fusion and by using a dry chemicalreagent (flux). This method is still believed to be the cheapest andmost accurate method of testing the gold content to date even theability of this method can match the testing of gold content usingx-ray machines. The accuracy of the fire assay method can reach0.04%, and is ideal if done on objects with gold content between33%-92%. Fire assay method is more emphasis on the propertiesof metals in certain conditions of temperature and chemical prop-erties. Broadly speaking the fire assay method is divided into 6major processes namely (12):

2.2.1 Sample Preparation

The concentrated sample is of the crystal form so that in the prepa-ration there is only a milling stage to ensure that the sample is 200mesh.

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2.2.2 Fluxing (Flux Addition)

Flux can be defined as a reaction / reagent added to a substance ormaterial that cannot or is difficult to melt to form a mixture thatcan be easily melted. The melting mixture is called slag (ore slag).Reagents in the flux contain various chemical compositions such asNa2CO3, P bO, SiO2, Na2B4O7, and CaF2.

2.2.3 Fusion (Consolidation)

Fusion of flux mixed sample, potassium nitrate and silver are meltedat 1050◦C in a fusion furnace. The required time ranges from 45to 60 minutes. Temperature must be maintained because if thetemperature is too low it can lead to imperfect gold and silveraccumulated in the lead liquor and will also produce small leadbutton. After the process of melting the lead liquor is poured intoa lead-button cone mortar and the slag will be separated, after thecold lead button is removed by hammering the slag of the mold.

2.2.4 Cupellation (Separation of Pb)

The separation of gold and silver from the lead button in the cupel iscarried out by means of a warming where the lead will be absorbedby the cupel and the remaining granules of gold and silver. Theheating temperature is 900-950 ◦C for 1 hour. The oxidized leadbutton to Pb metal is 98.5% absorbed into the cupel and 1.5%would be evaporates.

2.2.5 Bulking

Before the process of adding acid, the seeds prill flatted until mea-suring ±0.2 mm. This process aims to obtain perfect gold whendiluted with acid

2.3 Digestion (Dissolution)

Separation of gold and silver is done by adding nitric acid to silverdissolve. After the silver is completely dissolved and then addedwith 65% hydrochloric acid to dissolve the minerals still containedin gold by heating.

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The fire assay is the most employed method for determining goldin geological material. This method enables a high pre-concentrationbefore quantification and allows precise as well as accurate deter-mination of gold. The research have been conducted such as com-paring three analytical methods based on the atomic absorptiondetermination of gold following classical fire assay, the aqua regialeach and the sodium cyanide leach (13).

3 Methodology/Materials

3.1 Materials and Tools

The tools used in this test include fusion furnace, muffle furnace,multipour set (loader + mould + unloader), test tubes 10 mL, hotplate with a water bath, analytical balances d = 1 mg, crucible,cupel 8A & 6A and Atomic Absorption Spectrophotometer. Thematerials used in this test include sample concentration, sampleSTD G. 905 6, Flux (Na2CO3, P bO, SiO2, Na2B4O7, CaF2, flour,KNO3 and NaCl), concentrated hydrochloric acid, potassium ni-trate, nails, silver, concentrated nitric acid and distilled water.

3.2 Analysis of concentrate by gravimetric

A total of 15 grams of sample is inserted in a plastic bag with0.5 gram weight is then added 200 grams of flux and 18 grams ofKNO3 then inserted into crucible which contains 2 mg of silver.The sample is melted in a furnace at a temperature 1050◦C for45 minutes. The resulted molten iron poured into a mold, allowedcooling to form two phases which leads button (below), slag (above)which are then separated from the slag layer button lead. Slag willbe washing while lead button moved into cupel 8A.

3.3 Washing process

The slag put into crucible then added 25 grams of flux washing and10 grams of wheat flour and then merged back with 1050◦C temper-ature for 45 minutes, the result of molten iron is poured into a mold.The re-melting test samples left at room temperature to form twophases which leads button (below), slag (top) and separated lead

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button of slag. Lead button moved into cupel 8A which alreadycontain lead button of the first smelting process and slag (impuri-ties) disposed of in the waste. Furthermore, the separation of goldand silver from lead button with cupellation process with 950◦Ctemperature for 60 minutes until the process is perfect complete.The prill seeds flattened until the size of± 0.2 mm then resultedproduct put into crucible.

The prill seeds added 65% nitric acid solution (1: 5) 10 mL,then heated to a temperature 90-100 ◦C for 20-30 minutes. Furthersamples were rinsed 3 times with distilled water, and added 65%nitric acid solution (1: 1) 10 mL. The prill seed reheated for 30-45minutes then rinsed four times with distilled water and added 1-2mL of 65% hydrochloric acid solution for 3-5 minutes. The prillseeds rinsed again 4 times with distilled water, then re-heated anddried for 10 minutes. After the addition of acid, the prill seedsincluded in muffle furnace with 900◦C for 10 minutes, then cooled,dried and weighed using the analytical balance.

3.4 Analysis of cupel loss by spectrophotomet-ric

The cupel loss sample reduced to 200 mesh with ship loading toolauto sampler, then cupel loss sample weighed as much as 15 grams(duplo). The samples added 2.5 g sample STD G. 905 6 then in-serted into a plastic bag and added 150 g of flux. The samples weremixed until homogeneous and then put into crucible and addedspikes. The cupel loss sample inserted into the furnace to a tem-perature suitable melting process steps, namely 830, 880, 950, 980and 1050 ◦ C and then the sample poured into a mold of iron. Fur-thermore, the sample cooled into ambient temperature until formedtwo phases which leads button (below), slag (above).

Lead button included into cupel 6A for cupellation process,which is heated to a temperature of 950 C for 60 minutes, untilthe prill seed formed. Furthermore prill seeds were transferred toa test tube and then added 10 mL of 65% nitric acid solution, anddo warming to a temperature of 100 ◦C to dissolve prill. Cupelloss added 1 mL of concentrated hydrochloric acid and heated toa temperature of 100 ◦C until the yellow color vapor disappearedthen added distilled water muted and to mark boundaries and ho-

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mogenized. The cupel loss samples were analyzed using atomicabsorption spectrophotometry (AAS) at a wavelength of 242 nm.

4 Results and Findings

4.1 Gold separation by fire assay

Fire Assay is a quantitative analysis method to determine the metalcontent in rock and metallurgical products such as gold, silver andplatinum group metals. Fire assay method involves the dry chem-ical reagents or flux and the assay done by gravimetric based onthe heavy metals mass in a pure state (8). The stages of fire assaymethod includes sample preparation, the addition of flux, smelting,cupellation, the separation of gold and silver, partings and weigh-ing. Smelting process coupled with flux, which is a substance thatbinds impurities and to form a substance that is easy to melt, calledslag.

Figure 1. The smelting process

Sample preparation includes crushing the samples, milling ma-chines, and stirring. Samples were crushed until smooth reaches ±200 mesh size to obtain representative results. The addition of fluxwhich has a composition include Na2CO3, P bO, SiO2, Na2B4O7, CaF2,and flour aims to make the process of fusion by binding to sub-stances which are not desirable as a metal oxide (SiO2 and TiO2)and sulfur, such as pyrite (FeS2) and chalcopyrite (CuFeS2) con-tained in the minera (12). The addition of potassium nitrate (KNO3)having an oxygen content, which oxygen is used to oxidize sulfides

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in the ore is high grade sulfide. The reactions that occur as shownbelow (12):

2KNO3(s) −→ 2KNO2(s) + O2(g)

4CuFeS2(s) + 9O2(g) −→ 2Cu2S(s) + 2Fe2O3(s) + 6SO2(g)

FeS2(s) + O2(g) −→ Fe2O3(s) + SO2(g)

Figure 2. Lead botton on cupel

Each of flux composition has function when smelting namelysodium carbonate (Na2CO3) strongly alkaline material, reacts withthe sample to form alkali sulfide, aluminate and quartz. The oxi-dizer and sulfur removal is the next properties of sodium carbon-ate. The alkaline properties of lead (II) oxide (PbO) is weaker thansodium carbonate, but still good as oxidizing sulfur, when PbO isreduced in the melt to produce Pb which acts as a collector of pre-cious metals. Silicon dioxide (SiO2)is a very common substancefound in rocks, strongly acidic which will form quartz with metaloxides. Silicon dioxide is added when low levels of ore to producethe molten quartz more fluid and protect the cup from PbO at-tacks. Meanwhile borax (Na2B4O7)is also a strong acid, capableof dissolving all of a metal oxide. The ability to lower the melt-ing point to the fire assay process is another advantage of borax.Calcium fluoride (CaF2) serves to increase the fluidity of the melt,is used when the sample has Al content of more than 1%. Flour(flour) serves as a carbon source to reduce PbO into Pb importantin collecting precious metals(14).

Samples included in the concentrate to smelting furnace at atemperature of 1050 ◦ C to melt the metals, concentrates includedin the iron mold and cooled. In the process of fusion reaction wouldlead oxide oxidizing sulfur in the iron sulfide that the iron sulfideundergoes desulfurization to form metals oxide. While the sodiumcarbonate reacts with sulfur into sodium sulfate. The addition

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of sodium carbonate to prevent sulfur binds lead into lead sulfide(PbS) in the form of black sediment, so that the metal impuritiesare not oxidized. Borax hydrolyzed due to heating resulting borontrioxide. Metal oxides along with other impurities tied with borontrioxide formed a green colored glass called slag. The reaction ofthe melting process with the addition of flux as follows (8):

FeS2(s)+7PbO(s)+2Na2CO3(aq) −→ FeO(s)+7Pb(s)+2Na2SO4(aq)+2CO2(g)

Na2B4O7(aq) −→ Na2B2O4(l) + B2O3(s)

FeO(s) + B2O3(s) −→ FeB2O4(s)

Fire assay smelting process generates a metal precipitate, whichconsists of a variety of heavy metals that are not oxidized by PbO.Therefore it is necessary to separate more specifically with cupel-lation process which results into prill consisting of gold and silver.

In the process of washing gold analysis performed on a slag (im-purities) and put it back in crucible then added 25 grams of fluxwashing, and 10 grams of wheat flour samples of the concentrateback later merged with 1050 ◦C temperature for 45 minutes. Sam-ple concentrates washing iron is poured into molds and then cooled.Samples were cold separation slag and lead button by means solvedusing a spoon and lead button was added cupel 8A which alreadycontain lead button. Heavy metals will be under as a result ofdifferences in specific gravity is called the button. The precipitatealloy or lead is cleared physically is hit with a hammer on a bed ofiron. Lead button which has been separated from impurities wouldthen be analyzed the content of the gold in the sample. Slag (impu-rity) obtained in the melting process conducted advanced processcalled washing by adding a flux and flour to melted to obtain leadsbutton. The phase of lead button then had cupellation process toobtain prill seed which will be combined with the seed prill fromthe initial melting process.

4.2 Analysis of concentrate by gravimetric

The cupellation process was conducted after the lead has been cleanof impurities, at a temperature of 800-900◦C. The temperature,which is below the melting point of gold and silver, but above themelting point so that the Pb melts and is absorbed in the cupel,while precious metal will be deposited on the surface of the cupel

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which is often called prills. The resulted prill cooled and flattenedwith a hammer until the thickness of ± 0.2 mm. Gold and silver areseparated with the help of nitric acid 65% 1: 5 by 10 mL and thenheated in a fume hood with a temperature of 100◦C for 30 minutesfor the process to dissolve the silver. The prill seed after heating andthen washed with distilled water 3 times and added concentratedhydrochloric acid (1:1) for 1-2 mL and reheated for 15 minutes.The process of flushing the testing was conducted after addition ofnitric acid and hydrochloric acid prior to addition. This is doneto prevent any reaction between nitric acid with hydrochloric acid,because if nitric acid reacts with hydrochloric acid will be formedsolution aqua regia, where these solution are compounds that candissolve gold, so as to dissolve the silver without dissolving the goldto be tested, the rinsing process is done to prevent leaching of goldby aqua regia(15).

3Ag(s) + 4HNO3(l) −→ 3AgNO3(aq) + NO(g) + 2H2O(l)

Ag(s) + HCl(l) −→ AgCl(s) + H+(aq)

The addition of nitric acid used to dissolve silver in prill seedand separating the resulting silver ions to precipitate chloride afterthe addition of hydrochloric acid. The seed prill rinsed again withdistilled water 3 times, put in a furnace with a temperature of 900◦C for 15 minutes to evaporate the silver chloride and silver nitrateleft over from rinsing with distilled water, because silver chloridehas a melting point at a temperature of 455 ◦C and silver nitratehas a melting point with temperature of 212 ◦C, so that the heating900 ◦C silver chloride and silver nitrate will be lost and the onlyremaining pure gold. Pure gold is weighed using the analyticalbalance d = 0.1 mg, in order to more accurate results. The resultsof analysis of samples of concentrate using gravimetric fire assaycan be shown in Table 1 and the resulted product in Fig. 3

Figure 3. The gold from concentrate sample

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Table 1. Concentration of Concentrate Samples Using Gravimetric

Based on Table 1 gravimetric testing obtained an average goldweight on a sample of 0.216 g of concentrate. The concentrationof gold in the concentrate sample is obtained using the followingequation 1.

goldconcentration(mgg

) =goldweight(g)× 1000(mg

g)

weightofsample(g)(1)

4.3 Analysis of cupel loss by spectrophotomet-ric

The cupel loss used to be reanalyzed to view the gold content thatstill settles in cupel using fire assay by atomic absorption spec-trophotometry (AAS). The stages of fire assay methods includesample preparation, the addition of 2.5 g sample STD G. 905 6,the addition of flux, smelting, cupellation, the separation of goldand silver, and is measured using AAS. Smelting process coupledwith flux, which is a substance that binds impurities and to forma substance that is easy to melt, called slag. The addition of thegold standard in the sample cupel loss for gold content on a cupelloss is so small that when analyzed by AAS is not too good becauseoutside of the range of the standard curve calibration sequence thatshould be added to the standard.

Samples cupel loss in the form of prill seeds, added concentratednitric acid and heated to a temperature of 100 ◦C to dissolve prillseeds. Furthermore, concentrated hydrochloric acid was added in 1mL and heated to steam yellow disappears. The test sample is thencooled and added to mark boundaries distilled water volume of 10mL, then homogenized and measured using AAS with a wavelengthof 242 nm. Gold is resistant to nitric acid or hydrochloric acid, only

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aqua regia (hydrochloric acid: nitric acid, 1: 1) to dissolve it byforming anion tetrachloroaurate (III), and gain of hydrogen fromnitric acid that producing yellow gas nitrous oxide. The reactionof the addition of nitric acid and hydrochloric acid in the samplecupel loss is as follows(15).

Au(s) + 4HCl(l) −→ [AuCl4]−(aq) + 4H+

(aq)

[AuCl4]−(aq) + 4H+

(aq) −→ HAuCl4(aq) + NO(g) + 2H2O(1)

Table 2. Concentration Gold In Cupel Loss Using AtomicAbsorption Spectrophotometer (AAS)

Gold assays on samples cupel loss using standard addition methodfor gold content contained in cupel loss is so small that needs to beadded to the gold standard as much as 5 g. The gold standard isadded to the testing cupel loss can be determined by the followingequation 2.

goldstandardconcentration =weightofgoldstandard

weightofsample + weightofgoldstandard)×

5.96mg/L(2) Description: 5.96 mg/L = certified of samples STD Gcontent The results of the equation obtained by concentration ofgold is added by 0.85 mg/L. Gold concentrations in samples ob-tained from the measured cupel loss reduction from gold concen-trations and the concentration of the gold standard. Based on datashowed in Table 2, the average gold concentration in the cupel losswas 6.26×10−6 mg/g. The results of the analysis of the concentra-tion of gold in concentrate sample was added to the gold concentra-tion results in cupel loss to determine the total gold concentrationin the test sample. The result of the total gold content is shown inTable 3.

Table 3. Total Concentration of Gold

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Based on Table 3 obtained the average level of total gold was14.41 mg/g. The results of the analysis will be compared withthe concentration of gold standard samples which have been cer-tified. The average concentration of gold in concentrate standardwas shown in Table 4. The result suggested that the value of thegold content of the test sample included in the standard with amaximum of 14.86 mg/g.

Table 4. Gold Concentration on Concentrate Standard

4.4 Determination of precision and accuracy

Precision is the degree of similarity measurements proximity to oneanother. The precision is important to know whether or not a mea-surement based on the proximity of the measurement results withmeasurement repeatability. Meanwhile accuracy is the closeness ofthe measurement results with actual levels, so that the accuracyneeds to be determined to find out the accuracy of test results(9).The precision value of gold assay using a gravimetric can be shownin Table 5.

Table 5. Precision and accuracy values of gravimetric method

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The test is said to be precise if the value of RSD <2% and onthis test the RSD values obtained by 3.385%. The value of RSDobtained greater than 2%, so the need for determining the CV Hor-witz value tis important to figure out the level of precision in thistest. The CV Horwitz value obtained at 10.708%, which indicatesthat the gold assay with gravimetric method using fire assay is pre-cise due to the value of RSD < CV Horwitz. The determination foraccuracy test of gold by gravimetric is also conducted. Accuracy isthe closeness of test results with the right values, so the accuracyis quite good if the accuracy value entered between the range of80-110% (9). The accuracy value of the concentrate standard usinggravimetric are shown in Table 6.

Table 6. The Accuracy Test on Standard Concentrate

According to Table 6 of testing accuracy in the determinationof gold by gravimetric gold standard using 15 mg/g. The accu-racy value in the determination of gold by gravimetric amounted to99.06%. This result indicates the test has a good degree of accuracybecause the value entered in the range of 80-110%(9). The purposewas to determine the accuracy or closeness of test results with theright values. The determination of the precision and accuracy ofthe gold by using AAS can be shown in Table 7.

Table 7. The Precision and Accuracy Value

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The value of RSD obtained is 41.13 % which is greater than 2%, sothe CV Horwitz is further determined and resulted 34.329%, whichindicates that the gold assay in cupel loss with spectrophotometricusing fire assay is precise based on the value of RSD ¡CV Hor-witz. Meanwhile the accuracy in the spectrophotometric methodmeasured using % recovery. The test results said to be accurate ifthe% recovery value approaching 100%. Value% recovery obtainedin the determination of gold by AAS amounted to 99.88%, so theresult is said to be accurate because the value % recovery obtainedapproaching 80-110%.

4.5 Determination of LOD and LOQ

The gold assays on cupel loss using fire assay by Atomic AbsorptionSpectrophotometry (AAS), needs to be conducted to determine thelimit of detection (LOD) is the concentration or amount of thesmallest/lowest of the analyte in the sample can be detected, andthe limit of quantitation (LOQ) is quantification limit is defined asthe lowest concentration of the analyte in the sample, which can bedetermined with precision and accuracy that can be accepted onthe condition of operational methods used(10). The determinationof LOD and LOQ value aim to figure out the sensitivity of AASinstrument and resulted data can be seen in Table 8.

Table 8. The LOD and LOQ Value

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The LOD value for the measurement of concentration of gold isequal to 0.6146 mg/L, and the concentration LOQ value of goldis equal to 2.0488 mg/L, whereas the concentration of gold in thecupel loss before the addition of the gold standard that is equalto 0.121 mg/L. Gold concentrations in samples cupel loss is toosmall to meet the minimum limits on the concentration of LOD andLOQ, therefore the sample cupel loss should be added to the goldstandard addition with a concentration of 0.85 mg/L so cupel losscan be detected by AAS. The test resulted cupel loss concentrationafter the addition of gold standard was 0.97 mg/L.

5 Conclusion

Based on test results, it can be summed up as follows:1. The average gold content of the concentrate and cupel loss

prepared using fire assay respectively by gravimetric and spec-trophotometric were 14.41 mg/g and 6.27 ×10-6 mg/g.

2. The result of gold content analysis with gravimetric methodgave the precision value (% RSD) around 3.385, while the CV Hor-witz value was 10.708, and the accuracy with trueness value of99.06%. Meanwhile the spectrophotometric obtain the precisionvalue (% RSD) was 41.129 and the CV Horwitz around 34.329,while the value of accuracy (% recovery) of 99.88%, and the LODand LOQ values respectively were 0.6146 and LOQ 2.049.

Acknowledgement The authors are grateful to PT. Sucofindo(Persero) Timika Branch for fully supporting the materials and lab-oratory facilities also the permission to publish this work.

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References

[1] Klein C, Hurbult CS. Manual of Mineralogy 20th edition. NewYork: John Wiley&Sons Inc; 1985.

[2] Smith DW. Inorganic Substances: A Prelude to The Study ofDiscriptive Inorganic Chemistry. New York USA: CambridgeUniversity Press; 1990.

[3] Reddi GS, Rao CRM. Analytical techniques for the determi-nation of precious metals in geological and related materials.1999;124:1531-.

[4] Heurtebise M, Montoloy F, Lubkowitz JA. Rapid determi-nation of matrix components by neutron activation analysis,Analysis of gold alloys.45(1):47-.

[5] Brill M, Wiedemann KH. Determination of gold in gold jew-ellery alloys by ICP spectrometry. 1992;25:13-.

[6] Barefoot RR, Van Loon JC. Recent advances in the determi-nation of the platinum group elements and gold. 1999;49:1-14.

[7] Figueiredo AMD, Enzweiler J, Sarkis JE, Jorge AP, ShibuyaEK. NAA and UV laser ablation ICP-MS for platinum groupelements and gold determination in NiS fire assay buttons: acomparison between two methods. 2000;244:623-5.

[8] Haffty J, Riley LB, Goss WD. A Manual On Fire Assaying andDetermination of The Noble Metals In Geological Materials.1977.

[9] Riyanto. Validasi & Verifikasi Metode Uji. Yogyakarta: Deep-ublish; 2014.

[10] Kantasubrata J. Validasi Metode. Bandung: Pusat PenelitianKimia-LIPI; 2010.

[11] Turan A, Yucel O. The Effect Iron and Oxidizing Flux Addi-tion on The Fire Assay Of Low Grade Pyritic Refractory GoldOres. 2011;47(2):219-27.

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[12] Supriadidjaja A. Penentuan Kadar Emas (Au) Dan Perak (Ag)Metoda Fire Assay: Perbandingan Hasil Analisis PeleburanTungku Gas Terhadap Tungku Solar. 2007;1(1):51-9.

[13] Juvonen R, Kontas E. Comparison of three analytical methodsin the determination of gold in six Finnish gold ores, includinga study on sample preparation and sampling. 1999;65:219-29.

[14] Ronaldo I, Kurnia. Optimasi Teknik Fire Assay dan KondisiKupelasi Untuk Memperoleh Komposisi Fluks Terbaik PadaAnalisis Kadar Emas. 2014;15(1):55-62.

[15] Svehla. Buku Ajar Kimia Analisis Kuantitatif Anorganik.jakarta: Buku Kedokteran EGC; 1979.

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