Extraction of Lateritic Nickel Ore

(Hydrometallurgical Route)

Genesis And Types Of Nickel Laterites

Usually, nickel ore type in the world are sulphide and oxide minerals. In East Indonesia, we often see nickel oxide mineral that is called nickel laterite. Lateritic nickel ores formed by intensive tropical weathering of ultramafic rocks above all serpentinites which consist largely of the magnesium silicate serpentine and contains approx. 0,3% nickel. This initial nickel content is strongly enriched in the course of lateritization. Two kinds of lateritic nickel ore have to be distinguished: limonite types and silicate type.
1. Saprolite : Low iron (Fe), contains generally 1.5-2.5% nickel and consists largely of Mg- depleted serpentine in which nickel is incorporated. In pockets and fissures of the serpentinite rock green garnierite can be present in minor quantities, but with high nickel contents – Mostly 20-40%

Picture 1. Garnierite Picture

Picture 2. Serpentine

2. Limonite : High iron (Fe), consist largely of goethite and contain 1-2% nickel incorporated
in goethite.

Picture 3. Goethite

Route of Lateritic Nickel Ore Processing

There are 3 routes of lateritic nickel ore processing:
Pyrometallurgical route
1. Electric Smelting Furnace Technology
2. Krupp Renn Technology
3. Blast Furnace Technology

Hydro-Pyrometallurgical route
1. Caron Process
2. Modified Caron Process

Hydrometallurgical route
1. Atmosferic Leach
2. High Pressure Acid Leach (HPAL)
3. Acid Heap Leach
4. Chloride Leach

Comparation of these processes can be seen in table1.

Table 1. Comparation of Nickel Processing Technology

Experiments still be done by researcher to get the best process for limonitic ores. Until now, Caron Process & modified and HPAL is used by industry to extract nickel from limonitic ores. Flow diagram for Caron Process and HPAL can be seen in Figure 1-3.

Figure 1. Caron Process Flow Diagram

Figure 2. Modified Caron Process Flow Diagram

Figure 3. HPAL Process Flow Diagram

Proses Pengolahan Bijih Bauksit

Bijih bauksit merupakan mineral oksida yang sumber utamanya adalah:
1. Al2O3.3H2O, Gibbsit yang sifatnya mudah larut
2. Al2O3.3H2O, Bohmit yang sifarnya susah larut dan Diaspore yang tidak larut.

Berdasarkan data yang ada:

Sumber lain dari bijih bauksit:
Nephelin : (Na,K)2O.Al2O3.SiO2
Alunit : K2SO4.Al2(SO4)3.4Al(OH)3
Kaolin & Clay : Al2O3.2SiO2.2H2O

Cara-cara Leaching:

a. Cara Asam (H2SO4)

Hanya dilakukan untuk pembuatan Al2(SO4)3 untuk proses pengolahan air minum dan pabrik kertas.
· Reaksi dapat dipercepat dengan menaikkan temperatur sampai 180 C (Autoclaving)
· KalsinasiCocok untuk lowgrade Al2O3 tetapi high SiO2 yang tidak cocok dikerjakan dengan cara basa.
· Hasil Basic-Al-Sulfat dikalsinansi menjadi Al2O3, kelemahan cara ini adalah Fe2O3 ikut larut.

b. Cara Sintering dengan Na2CO3 (Deville-Pechiney)

Sintering dilakukan dalam Rotary Kiln 1000 C selama 2-4 jam, cocok untuk bijih dengan high Fe2O3 dan SiO2.

Reaksi-reaksi:

Al2O3 + Na2CO3 = NaAlO2 + CO2(g)
Fe2O3 + Na2CO3 = Na2O∙Fe2O3 + CO2(g)
TiO2 + Na2CO3 = Na2O∙TiO2 + CO2(g)
SiO2 + Na2CO3 = Na2O∙SiO2 + CO2(g)

c. Cara Basa (NaOH), Proses Bayers (Th 1888)

Ada 2 macam produk alumina yang bisa dihasilkan yaitu Smelter Grade Alumina (SGA) dan Chemical Grade Alumina (CGA). 90% pengolahan bijih bauksit di dunia ini dilakukan untuk menghasilkan Smelter Grade Alumina yang bisa dilanjutkan untuk menghasilkan Al murni. Berikut block diagram pengolahan bauksit melalui proses SGA:

Gambar 1. Block Diagram Pengolahan Bauksit

Reaksi Pelindian:
· Mineral Bijih:

Al2O3∙3H2O + 2 NaOH = Na2O∙Al2O3 + 4 H2O (T =140 C, P= 60 psi)

· Impurities:

SiO2 + 2 NaOH = Na2O∙SiO2 + H2O (Silika yang bereaksi adalah silika reaktif)
2(Na2O∙SiO2) + Na2O∙Al2O3+2H2O = Na2O∙Al2O3∙SiO2 (Tidak larut) + 4 NaOH

Dalam proses ini dibatasi jumlah silika reaktifnya karena sangat mengganggu dengan menghasilkan doubel Na-Al-Silikat yang mempunyai sifat tidak larut. Fe2O3 dan TiO2 tidak bereaksi dengan NaOH dan tetap dalam residu (Red Mud), sedangkan V2O5, Cr2O3, Ga2O3 larut sebagai by product.

Reaksi Presipitasi:
Dilakukan dengan memanfaatkan hidrolisa karena pendinginan T=60-65 C sampai 38-43 C, t = 100 jam

Na2O3∙3H2O + 4 H2o = Al2O3∙3H2O(s) + 2 NaOH

Kalsinasi:

Al2O3∙3H2O = Al2O3(pure) + 3 H2O(g) (T=1200 C)

Proses Pengolahan Nikel Menjadi FeNi Dari Bijih Laterite

Secara umum, mineral bijih di alam ini dibagi dalam 2 (dua) jenis yaitu mineral sulfida dan mineral oksida. Begitu pula dengan bijih nikel, ada sulfida dan ada oksida. Masing-masing mempunyai karakteristik sendiri dan cara pengolahannya pun juga tidak sama. Dalam bahasan kali ini akan dibatasi pengolahan bijih nikel dari mineral oksida (Laterit).

Bijih nikel dari mineral oksida (Laterite) ada dua jenis yang umumnya ditemui yaitu Saprolit dan Limonit dengan berbagai variasi kadar. Perbedaan menonjol dari 2 jenis bijih ini adalah kandungan Fe (Besi) dan Mg (Magnesium), bijih saprolit mempunyai kandungan Fe rendah dan Mg tinggi sedangkan limonit sebaliknya. Bijih Saprolit dua dibagi dalam 2 jenis berdasarkan kadarnya yaitu HGSO (High Grade Saprolit Ore) dan LGSO (Low Grade Saprolit Ore), biasanya HGSO mempunyai kadar Ni ≥ 2% sedangkan LGSO mempunyai kadar Ni <>

Tabel 1. Contoh Komposisi Saprolit Ore

Berdasarkan table 1, faktor yang paling penting diperhatikan adalah basisitas (tingkat kebasaan) MgO/SiO2 atau ada juga yang mengukur berdasarkan SiO2/MgO. Tingkat kebasaan ini menentukan brick/ refractory/bata tahan api yang harus digunakan di dalam tungku (furnace), jika basisitas tinggi maka refractory yang digunakan juga sebaiknya mempunyai sifat basa agar slag (terak) tidak bereaksi dengan refractory yang akan menghabiskan lapisan refractory tersebut. Basisitas juga menentukan viscositas slag, semakin tinggi basisitas maka slag semakin encer dan mudah untuk dikeluarkan dari furnace. Namun basisitas yang terlalu tinggi juga tidak terlalu bagus karena difusi Oksigen akan semakin besar sehingga kehilangan Logam karena oksidasi terhadap logam juga semakin besar.

Gambar 1. Kesetimbangan Metal-Slag

(Ket: Slag selalu berada di atas metal karena densitynya lebih rendah)

Secara umum proses pengolahan bijih nikel jalur pyrometallurgy dibagi dalam beberapa tahap seperti dalam diagram berikut:

Gambar 2. Diagram alir proses

1. Kominusi
Kominusi adalah proses reduksi ukuran dari ore agar mineral berharga bisa terlepas dari bijihnya. Berbeda dengan pengolahan emas, dalam tahap kominusi untuk nikel ore ini hanya dibutuhkan ukuran maksimal 30 mm sehingga hanya dibutuhkan crusher saja dan tidak dibutuhkan grinder.

2. Drying
Drying atau pengeringan dibutuhkan untuk mengurangi kadar moisture dalam bijih. Biasanya kadar moisture dalam bijih sekitar 30-35 % dan diturunkan dalam proses ini dengan rotary dryer menjadi sekitar 23% (tergantung desain yang dibuat). Dalam rotary dryer ini, pengeringan dilakukan dengan cara mengalirkan gas panas yang dihasilkan dari pembakaran pulverized coal dan marine fuel dalam Hot Air Generator (HAG) secara Co-Current (searah) pada temperature sampai 200 C.

3. Calcining
Tujuan utama proses ini adalah menghilangkan air kristal yang ada dalam bijih,air kristal yang biasa dijumpai adalah serpentine (3MgO.2SiO2.2H2O) dan goethite (Fe2O3.H2O). Proses dekomposisi ini dilakukan dalam Rotary Kiln dengan tempetatur sampai 850 oC menggunakan pulverized coal secara Counter Current. Reaksi dekomposisi air kristal yang terjadi adalah sebagai berikut:

a. Serpentine

Reaksi dekomposisi dari serpentine adalah sebagai berikut:

3MgO.2SiO2.2H2O = 3 MgO + 2 SiO2 + 2 H2O

Reaksi ini terjadi pada temperatur 460-650 C dan tergolong reaksi endotermik. Pemanasan lebih lanjut MgO dan SiO2 akan membentuk forsterite dan enstatite yang merupakan reaksi eksotermik.

2 MgO + SiO2 = 2MgO.SiO2
MgO + SiO2 = MgO.SiO2

b. Goethite

Reaksi dekomposisi dari goethite adalah sebagai berikut:

Fe2O3.H2O = Fe2O3 + H2O

Reaksi ini terjadi pada 260C – 330C dan merupakan reaksi endotermik.

Di samping menghilangkan air kristal, pada proses ini juga biasanya didesain sudah terjadi reaksi reduksi dari NiO dan Fe2O3. Dalam teknologi Krupp rent, semua reduksi dilakukan dalam rotary kiln dan dihasilkan luppen. Sedangkan dalam technology Electric Furnace, hanya sekitar 20% NiO tereduksi secara tidak langsung dalam rotary kiln menjadi Ni dan 80% Fe2O3 menjadi FeO sedangkan sisanya dilakukan dalam electric furnace.

Produk dari rotary kiln ini disebut dengan calcined ore dengan kandungan moisture sekitar 2% dan siap dilebur dalam electric furnace.

4. Smelting
Proses peleburan dalam electric furnace adalah proses utama dalam rangkaian proses ini. Reaksi reduksi 80% terjadi secara langsung dan 20% secara tidak langsung pada temperature sampai 1650 C. Reaksi reduksi langsung yang terjadi adalah sebagai berikut:

NiO(l) + C(s) = Ni(l) + CO(g)
FeO(l) + C(s) = Fe(l) + CO(g)

Beberapa material yang mempunyai afinitas yang tinggi terhadap oksigen juga tereduksi dan menjadi pengotor dalam logam.

SiO2(l) + 2C(s) = Si(l) + 2CO(g)
Cr2O3(l) + 3C(s) = 2Cr(l) + 3CO(g)
P2O5(l) + 5C(s) = 2P(l) + 5CO(g)
3Fe(l) + C(s) = Fe3C(l)

Karbon disupplay dari Antracite (tergantung desain), dan reaksi terjadi pada zona leleh elektroda. CO(g) yang dihasilkan dari reaksi ini ditambah dengan CO(g) dari reaksi boudoard mereduksi NiO dan FeO serta Fe2O3 melalui mekanisme solid-gas reaction (reaksi tidak langsung):

NiO(s) + CO(g) = Ni(s) + CO2(g)
CoO(s) + CO(g) = Co(s) + CO2(g)
FeO(s) + CO(g) = Fe(s) + CO2(g)
Fe2O3(s) + CO(g) = 2FeO(s) + CO2(g)

Oksida stabil seperti SiO2, Cr2O3 dan P2O5 tidak tereduksi melalui reaksi tidak langsung. Sampai di sini Crude Fe-Ni sudah terbentuk dan proses sudah bisa dikatakan selesai.

Yield (recovery) dari nikel pada EAF dapat didekati seperti pada gambar berikut:

Gambar 3. Hubungan antara Fe yield dan Ni yield dalam EAF

Gambar 4. Hubungan antara Fe yield dan %Ni dalam Crude FeNi

Gambar 5. Diagram fasa biner Fe-Ni

Pada daerah interface (antar muka) Slag-Metal terjadi kesetimbangan sebagai berikut:

Si(l) + 2FeO(l) = 2Fe(l) + SiO2(l)
Si(l) + 2NiO(l) = 2Ni(l) + SiO2(l)
NiO(slag) + Fe(metal) = Ni(metal) + FeO(slag)

Sekali lagi basisitas sangat penting dalam kondisi ini, sebagai contoh proses yang didesain dengan basisitas 0,68 maka:

MgO = 0.68SiO2

MgO + SiO2 = 100%
0.68SiO2 + SiO2 = 100%
1.68SiO2 = 100% ®
SiO2 = 59.5% dan MgO = 40.5%

Korelasi antara slag melting point pada SiO2 59.5% dan MgO 40.5% diilustrasikan oleh diagram terner FeO-MgO-SiO2 dalam gambar 6 (diambil dari Slag Atlas, Verlagstahleisen, M.B.H., Duesseldorf, 1981 and I.J. Reinecke and H. Lagendikj, INFACON XI Conference Proceeding, 2007).

Gambar 6. Diagram terner FeO-MgO-SiO2 yang menunjukkan hubungan antara slag melting point dan slag basicity of 0.68 & 0.5 untuk FeO 6% & 10%

5. Refining
Pada proses ini yang paling utama adalah menghilangkan/memperkecil kandungan sulfur dalam crude Fe-Ni dan sering disebut Desulfurisasi. Dilakukannya proses ini berkaitan dengan kebutuhan proses lanjutan yaitu digunakannya Fe-Ni sebagai umpan untuk pembuatan Baja dimana baja yang bagus harus mengandung Sulfur maksimal 20 ppm sedangkan kandungan Sulfur pada Crude Fe-Ni masih sekitar 0,3% sehingga jika kandungan sulfur tidak diturunkan maka pada proses pembuatan baja membutuhkan kerja keras untuk menurunkan kandungan sulfur ini.

Proses ini dilakukan pada ladle furnace dengan agent sebagai berikut:

Tabel 2. Agent Untuk desulfurisasi

Sedangkan reaksi yang terjadi adalah sebagai berikut:

CaC2 (S) + S = CaS (S) + 2C (Sat)
Na2CO3 + S + Si = Na2S + (SiO2) + CO
Na2Co3 + SiO2 = Na2O . SiO2 + CO2

Reaksi ini merupakan reaksi eksotermik sehingga tidak membutuhkan pemanasan lagi pasca smelting.

Proses selanjutnya adalah converting, sebenarnya proses ini masih dalam bagian refining hanya untuk membedakan antara menurunkan sulfida dengan menurunkan pengotor lain seperti Si, P, Cr dan C sesuai dengan kebutuhan. Sedangkan prosesnya sama hanya saja reaksi lebih dominan oksidasi dari oksigen.

Si (l) + O2 (g) = SiO2 (l) ↔ SiO2 (l) + CaO (l) = CaO . SiO2 (l)
Cr (l) + 5O2 (g)= 2Cr2O3 (l)
4P (l)+ 5O2 (g)= 2P2O5 (l) ↔CaO (l)+P2O5 (l)= CaO. P­2O5 (l)
C(l) + ½ O2 (g)= CO (g)
C(l) + O2 (g)= CO2 (g)


Tabel 3. Contoh Komposisi Crude Fe-Ni yang dihasilkan

Extraction Process of Gold (Au) and Silver (Ag)

Generally, extraction process of all metal always include the Comminution (Size Reduction)to liberate achieve mineral. The next process of gold extraction from Hydrometallurgy route is Leaching. There are reagents that can be used to gold leaching process: Mercury (Hg), Cyanide (CN-) usual as KCN or NaCN, Thiosulphate (Na2S2O3), and Thiourea.
Reagent vote for leaching process depend on:
1. Kind of Ore
2. Grade of Gold in the Ore
3. Cost
4. Material Handling
5. Government Regulation
Until now, the most reagent for gold leaching process in Industry is Cyanide (CN-) although hazardous material. It’s caused by highest recovery of gold (>95%), short time process, and more economize.

In the next time, the position of cyanide will be changed by another reagent that environmental friendly but the recovery of gold still high. many reagents being tried by researcher and Thiosulphate is the best reagent to change cyanide. Based on our research, thiosulphate give high gold recovery for Oxide and Sulphide Gold Mineral although the consumption of this reagent higher than cyanide. But thiosulphate is more environtmental friendly and cash cost can be lower because there is not additonal cost such as cyanide destruction. The problem for this reagent is about stabilisation. Thiosulphate is not stable hence need a good process controlling.

Below is the flowsheet of gold extraction process in industry:

Concentration

The Concentration process will be done when many native gold in the ore. Native gold will not break by grinding / milling, it will be changed to another shape, float on the slurry and go together to the tailing dam before be leached perfectly.

There are many concentration method, the most method that often be used: Humphreys Spiral, Shaking Table, or Jigging. This method work by the difference of density between gold and impurities hence cost of production lower. The Advance of gravity concentration is Knelson Concentrator

Leaching

There are many theory of the gold leaching: Elsner’s Oxygen Theory, Janin’s Hydrogen Theory, Bodlanders’s Hydrogen Peroxide Theory, Boonstra’s Corrosion Theory, until Kinetic proving Theory by Habashi. Elsner’s Oxygen Theory is The most of theory that used, reaction of gold and silver leaching:

2Au + 8NaCN +O2 + 2H2O = 4NaAu(CN)2 + 4NaOH
2Ag + 8NaCN +O2 + 2H2O = 4NaAg(CN)2 + 4NaOH

Below is the mechanism of reaction in a electrochemical cell :

The process parameter of leaching :
1. Particle Size
Depend on mineral, usually 80-90% -200 mesh (-74 micron)

2. Cyanide Strength
> Cyanide strength make > kinetics of reaction. Usually 750-850 ppm NaCN, depend on mineral.
3. Dissolved Oxygen (DO)
Generally, > DO make > kinetic of reaction depend on mineral. But based on limiting theory, the cyanide-DO ratio is 6 (constant). So if we use cyanide excess, the kinetic of reaction is controlled by dissolved oxygen. Usually, standard parameter for dissolved oxygen is 6-8 ppm.

4. pH 10-10,5
If pH<10>10,5, the possibility is: H2O2 will be formed and recovery also decrease.

5. %-Solid
> %-solid make gold and silver recovery decrease. If %-solid is too low, maybe gold recovery will increase but cyanide consumption will increase significantly. Beside that production capacity will decrease. Usually, many industry operate %-solid between 40-50%-weight.

6. Temperature
> Temperature make > kinetic of reaction, but limited by Dissolved oxygen. Because >Temperature make dissolved oxygen decrease. Usually, process temperature is not controlled.

7. Retention Time
> Retention time make gold recovery increase but production capacity decrease. Usually, retention time for gold processing about 48 hours.

Route 1
Adsorption

This process is the first process from gold recovery. There are many kind of adsorbans that can be used, activated carbon, zeolit, or resin. Common adsorban in many gold processing industry is activated carbon. Several factor to choose activated carbon are:
1. Hardness/attrition resistant
2. Activity
3. Total gold capasity adsorption
4. Shape and size distribution
5. Ash content
6. Bulk Density
7. Moisture
8. Surface area
9. %-Carbon Tetrachloride (CCl4)
10. %-w/wt Benzene adsorption
Hardness/attrition resistant is the most important, beside that activity and total gold capacity adsorption also important.

Elution

Elution process is divorce of complex Au(CN)2- and Ag(CN)2- from activated carbon. There are many standard than can be used, depend on mineral and adsorban. Common elution method is AARL (Anglo American Research Laboratory). This elution standard is divided to 6 stage:
1. Acid Wash
The aim of acid wash is solute of carbonate (CO32-), usually in calcium carbonate (CaCO3) form. HCl 3% is used at this stage and the reaction is :

CaCO3 + 2HCl =CaCl2 + CO2 + H2O

Beside this acid, we also can used the other acid for example: HNO3. because this acid more oxidative than HCl, so we must control well in order that the carbon (CO) is not oxidized to CO2.

2. Water Wash
This stage only for Carbon cleaning from HCl.

3. Pretreatment /Presoak
Absolutely, pretreatment/presoak is the first process for divorcing Au and Ag from activated carbon (C-Au(CN)2-). NaOH 3% and NaCN 3% are used in this process at 80-90 C.

4. Recycle Elution
after C-Au(CN)2- is divorced, water recycle is flowed at 100-120oC and pressure 300-400 Kpa. Water from elution column is Pregnant Solution and ready to next process (Electrowinning)

5. Water Elution
6. Water Cooling

At stage 5 and 6, water from elution column enter to recycle tank for next recycle elution.

Electrowinning
The Principle of electrowinning is metal sedimentation from pregnant solution by electricity. Direct current is used in this process hence resulting reduction-oxidation reaction at electrode:
1. Anode
Oxidation reaction always:

2H2O =O2 + 4H+ + 4 e

Because of H+ formed, pH-solution decrease and HCN gas will be formed. This gas is corrosive and the consumption of anode will increase hence we must control pH-solution more than 12,5.

2. Cathode
Reduction reaction always:

Au+ + e = Au and Ag+ + e = Ag

Sum total of cathode is more than anode:

Cathode = Anode +1

Voltage and current for electrowinning can be got by Nerst’s equation. The product of electrowinning process is cake and then ready to be smelted.

Route 2
Precipitation
Precipitation can be done for clarified pregnant solution. Before precipitation, solid-liquid separation is done at thickener. Usually, we use CCD Thickener (Counter Current Decantation).

Precipitation can be done by many method:
1. Gas precipitation
2. Ion exchange precipitation
3. Cementation
Cementation is the most popular method. In the cementation method, metal powder is used to reduction of achieve metal. Commonly, Zn powder is used for gold cementation. Metal with lower potential reduction can be used in cementation process:

Li, K, Ba, Ca, Na, Mg, Al, Zn, Cu, Fe, Pb, Ag, Pt, Au.

For example : if we want to get Au and Ag, we must add Pb, Fe, Cu, Zn etc. Al can not be used for cyanide complex Au(CN)2- because Al oxide is protective hence reduction reaction finished. The reaction of gold cementation by Zn is :

Au+ + Ag+ + Zn = Au + Ag + Zn2+

The product of cementation is cake and ready to smelting process.

Smelting

Smelting process work at 1200 C, borax (Na2B4O7•10H2O) added as flux to retain slag and increase of basicity hence tapping can be done easier. The product of smelting process is Dore bullion (Au-Ag alloy).

Refining
Refining process is done to get pure gold (99,99%). Usually, there are two method that used by refinery industry:
1. High Ag Bullion
Electrorefining is the first process, the principle of electrorefining is the same as electrowinning. But anode for this process is Bullion, and AgNO3 is the solution. Silver will be at cathode and gold at anode, then smelting process is done to get gold and silver bar.

We must do the electrolysis to get 99,99%, the solution of gold electrolysis is Au(Cl)2-.

2. High Au Bullion
Bullion is smelted directly with flowing Cl2 gas, chloride gas will retain Au and we will get Au and Ag bar.

We also have to do the electrolysis to get 99,99%, the solution of gold electrolysis is Au(Cl)2-.

Extraction Process For Pb and Zn from Galena (PbS) and Sphalerite (ZnS) Ores

In the world, usually Galena ore (PbS) is found together with Sphalerite ore (ZnS) in sulfide mineral. The Grade of PbS and ZnS in the ore between 2-8% for PbS and 8-16 % for ZnS. Generally, to increase the concentration of the metal in sulfide mineral is used The Froth Flotation.

Froth Flotation is Physical Chemistry methode to separate achieve mineral and impurities by use the mineral interface difference. The mineral that is very easy to absord the water is called by Hydrofillic, and the other is Hydrofobic. The Hydrofillic particles will be in the pulp, and the others will be at the air bulb and flow to the atmospheric surface. Usually, we use the reagents to make the interface particles become hydrofillic or hydrofobic. The reagents that we use in flotation are: collector, frother and modifier such as activator, pH regulator, depresant dan dispersant.

Figure 1. Scheme of froth flotation in Denver Flotation Cell

Below is the function for the reagents :
1. Collector
Collector is the reagent that make mineral surface become hydrophobic. Usually, colector is heteropolar organic mineral, content polar and non-polar side. Non-polar side is hydrofobic and will be at the air bulb, and polar side will be at specific solid particles than the solid particles will go to atmospheric surface.

2. Frother
When the surface of the specific solid particle become hydrophobic, that particle must converge with the air bulb from aeration. But the problem is the air bulb will be broke by hit with solid particle, cell, and the other air bulb. So, to make the air bulb become the stable bulb, we must add frother to the pulp. Frother is the reagent that can decrease the surface tension of the bulb hence the bulb is stable. The Effective Frother usually content minimum 5 atoms of carbon in the main molecule.

Table 1. The Frothers that often be used

3. Modifier
Modifier such as : activator, depressant, dispersant and pH regulator often be added to the flotation process. Activator is the reagent that used to increase interaction between solid particle and collector. Depressant make chemist polar film on the surface of the solid particle hence more hydrofobic. Dispersant is used to avoid the agglomeration, hence the particle can interact with the collector and the air bulb well. pH regulator is used to control of pH in order that the hydrofobic system can work optimally.

In Froth flotation for galena and spalerite, the reagents that be used :
1. Xanthate as collector
2. Pine Oil as frother
3. CaO as pH Modifier
4. CuSO4 as Activator for Pb
5. ZnSO4 as Activator for Zn
Generally, Flotation process for PbS and ZnS on industry scale is done continuously. Flowsheet of the process can be seen in figure 2.

Figure 2. The Flowsheet of the flotation process

Based on flowsheet in figure 2, we can see that we get 4 kinds of concentrates:
1. Cons. PbS
2. Cons. Mix PbS and ZnS
3. Cons. ZnS
4. Cons. Sulfur
All these concentrates will be processed to get the end product.. Cons. Sulfur is often processed by oxydation become H2SO4, the reaction:

S + O2 = SO2
SO2 + 1/2 O2 + H2O = H2SO4

Sulfur can be processed to the other product too, for example: fertilize, soap, medicine etc.

After concentration be done, then extraction process for Pb and Zn from the concentrates. We can used pyro ore hydro route, but we will discuss about pyrometallurgy route. Generally, in pyrometallurgy route, the concentrate converted to pellet. The aim of this process is avoid many dust in roasting and smelting process.

Figure 3. Extraction process flowsheet of Zn and Pb from consentrate ZnS

The same process is also done for concentrate PbS and mix PbS-ZnS. The dominant reactions of roasting and smelting process are :

ZnS + 3/2 O2 = ZnO + SO2
PbS + 3/2 O2 = PbO + SO2
C + 1/2 O2 = CO
ZnO + PbO + 2CO = Zn + Pb + 2CO2

The dominant reactions of electrowinning process for crude Pb are :

Pb + H2SO4 + 1/2 O2 = PbSO4 + H2O
Pb2+ + 2e = Pb
2H2O = 4 H+ + O2 + 4e
2H2O + 2e = H2 + 2OH-
2H+ + SO42- = H2SO4

Actually the metals that more achieve such as Cadmium (Cd), Antimony, Bismut etc that we say as impurities can be extract in this process with a little additional treatment.

Extraction process of Pb and Zn from their ore is not availabe yet in Indonesia. But may be in the next year will be build by PT. Dairy Prima Mineral (One of Antam’s subsidiary at North Sumatra). One of the established process in China is Zhongjin Lingnan Nonfemet Co. Ltd