Molibden konsantrelerinin değerlendirilmesi
Evaluation of molybdenum concentrates
Yazar: KAĞAN BENZEŞİK
Danışman: PROF. DR. ONURALP YÜCEL
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı / Üretim Metalurjisi ve Teknolojileri Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2016
Konu: Metalurji Mühendisliği = Metallurgical Engineering
Dizin: Hidrometalurji = Hydrometallurgy ; Pirometalurji = Pyrometallurgy ; Üretim metalurjisi = Production metallurgy

Özet:
Bu tez çalışmasının amacı, yerli molibdenit (MoS2) konsantresinden hareketle, çeşitli
molibden ürünleri üretiminde başlangıç malzemesi olabilecek kalitede molibden
trioksit üretilmesidir.
Çalışma konusu kapsamında, total oksitleyici kavurma yöntemiyle molibdenit
konsantresinden molibden trioksit (MoO3) eldesi ve saflaştırma işlemleri yapılmıştır.
Saflaştırma işlemi mevcut bakırı uzaklaştırmak için hidrometalurjik yöntemle
gerçekleştirilmiştir. Ayrıca, WindowsTM tabanlı termokimyasal bir bilgisayar
programı olan FactSage ile termodinamik hesaplamalar yapılmış ve ürünlerin
karakterizasyon çalışmaları tamamlanmıştır.
Deneysel çalışmalarda Özdoğu İnş. ve Tic. Ltd. Şti.. iştiraki Kuzey Ege Bakır
İşletmeleri tarafından gönderilen MoS2 konsantresi kullanılmıştır. Özdoğu İnş. ve
Tic. Ltd. Şti., ağ.% 0,40 Cu ve ağ.% 0,05 Mo içeriğine sahip tüvenan cevheri
flotasyon ile zenginleştirerek ağ.% 27 Cu ve ağ.% 52 Mo içeriğine sahip iki ayrı
konsantre elde etmektedir.
Deneysel çalışmaların birinci aşamasında MoS2 konsantresine total oksitleyici
kavurma deneyleri uygulanmıştır. Deneyler kamaralı tip fırında yapılmış olup, farklı
sıcaklıklarda ve sürelerde kavurma işlemi uygulanarak, kavurma sıcaklığı ve
süresinin, MoS2'nin MoO3'e dönüşüm hızı ve bileşimine etkisi incelenmiştir.
Deneyler sonucunda farklı kalitelerde MoO3 ürünleri elde edilmiştir. Deney sonuçları
incelenerek teknik kalite MoO3 standartlarına en uygun MoO3 üretimini sağlayan
sıcaklık ve süre parametreleri saptanmıştır. Artan sıcaklık ve sürenin, ürünlerdeki
kükürt miktarına azaltıcı bir etki yaptığı gözlemlenmiştir. Başlangıçta ağ.% 39,19
kükürt içeriğine sahip MoS2 konsantersinin kavrulması sonucunda elde edilen MoO3
ürünlerinin kükürt içeriği % 1,05'e kadar düşürülmüştür.
Deneysel çalışmaların ikinci kısmını oluşturan hidrometalurjik saflaştırma
deneylerinde, teknik kalite MoO3 standartlarına en uygun ürünleri veren kavurma
parametreleriyle üretilen MoO3 numuneleri liç işlemine tabi tutulmuştur. Sülfürik
asit çözeltisi ile yapılan liç deneylerinde, çözelti konsantresi ve katı-sıvı oranının,
metal kazanımına etkisi incelenmiştir. Deneyler sonucunda MoO3 ürünlerinin bakır
içeriği ağ.% 0,13'e kadar düşürülmüştür. Molaritenin artması ve katı sıvı oranının
azalması metal kazanım verimini arttırmıştır.
Karakterizasyon çalışmaları kapsamında elde edilen ürünlere kimyasal analiz, XRD
ve AAS teknikleri uygulanmıştır.

Abstract:
The aim of this study is processing of local molybdenum concentrate to produce
quality molybdenum trioxide may be the starting material for the production of
various molybdenum products.
Generally molybdenum metal is produced from its high grade sulphide ore through
oxidizing roasting of molybdenite (MoS2) in order to obtain molybdenum trioxide
(MoO3), purification of molybdenum trioxide and hydrogen reduction of
molybdenum trioxide.
Molybdenum concentrates which contain about 90 wt.% MoS2, along with up to
10 wt.% silicious material as well as traces of iron, copper and lead minerals, are the
main mineral of the molybdenum industry for the production of technical grade
molybdenum trioxide, which is further used to produce molybdenum,
ferromolybdenum alloys, molybdenum dioxide and other pure molybdenum
compounds such as ammonium dimolybdate, sodium and calcium molybdate.
The usual practice is to roast the concentrates with sufficiently low copper and lead
levels to produce a calcine that is essentially MoO3 containing low sulphur. Such
calcines can be used directly in steelmaking, because liquid iron will reduce MoO3 to
metal in high yield.
Molybdenum is widely used for the production of ferromolybdenum, which is
required for the production of alloyed steel. Almost 80 % of molybdenum, produced
from molybdenum trioxide, is used for steel making in industries.
Technical-grade MoO3 is produced by roasting molybdenite in air atmosphere in a
multiple-hearth furnace. The roasted MoO3 product usually has <0.1% sulfur content.
The multiple-hearth furnace is used because the hearths can be segmented to
accomplish specific and different conversion operations within a single unit.
In the upper hearths of the furnace, flotation oils are burnt off and water is
evaporated. This part of the process is usually augmented by burning fossil fuels to
ensure consistent temperature control and uniform roasting throughout the remainder
of the unit. Upper hearth temperatures are between 600 and 700 ºC.
The majority of the sulfur is removed by oxidation in the intermediate hearths. Since
the sulfur oxidation reactions are highly exothermic, additional heating is not needed
in this part. The hearth temperatures are controlled between 600 and 650 ºC by the
addition of excess air and water spray cooling.
As sulfur burning is about to completed, the composition of the roaster hearth is
mostly MoO2 with <20 wt.% MoO3 and MoS2 contents. The reaction of MoO3 with
MoS2 which forms MoO2, is driven by the strong oxidizing power of MoO3, so that the production of MoO3 is limited until most of the MoS2 is gone. Once the
availability of MoS2 is less than the availability of MoO3, MoO2 is quickly converted
to MoO3. Despite this reaction is exothermic, it is not sufficient to maintain the
temperatures above 525 ºC which are required to complete sulfur removal and
conversion to MoO3. So that additional heating is required in these lower hearths.
The oxide product is discharged from the roaster, cooled, and milled to form
technical grade MoO3. Technical-grade MoO3 typically contains 85–90 wt.% MoO3,
the balance being silica with some Fe2O3 and Al2O3.
In some cases, additional hydrometallurgical processing is needed to produce
technical-grade MoO3. In steel making, using molybdenum trioxide with high copper
content has some harmful effects on the mechanical properties of the alloyed steel
produced. Therefore, the up-gradation of molybdenum trioxide is required in steel
industry. The up-graded molybdenum trioxide must have less than 0.5 wt.% Cu
content for ferromolybdenum production.
Before the experiments, some thermodynamic simulations were made to determine
the optimum parameters for roasting and hydrometallurgical purification, with a
WindowsTM based thermochemical simulation program named FactSage. FactSage
allows us to make some complex process system simulations. And according to
databases of the program (Fact, FS, SGTE etc.), it is possible to simulate a large
number of compounds, alloys, molten systems and aqueous solution systems. In
FactSage, chemical reactions, pressure-temperature diagrams, Eh-pH diagrams of the
desired systems can be simulated. Also the phase diagram calculations of oxides and
alloys can be done and the results can be given as tables or graphics. FactSage is a
beneficial program in the areas of metallurgy and materials engineering, chemical
engineering, organic chemistry and environmental engineering.
In this study, molybdenum trioxide was obtained from local molibdenite concentrate
with the total oxidizing roasting method, the main impurity metal copper was leached
out from the obtained molybdenum trioxide with hydrometallurgical purification
process, thermodynamic calculations were made by a WindowsTM based
thermochemical simulation program named FactSage and characterization of the
products were completed.
The raw material which was used in total oxidizing roasting experiments, is local
molybdenite concentrate sent by Özdoğu İnş. Tic. Ltd. Şti. According to Özdoğu İnş.
Tic. plant production chief, the ore which has 0.40 wt.% Cu and 0.05 wt.% Mo
content, is subjected to a flotation process in order to obtain enriched two different
concentrates which have 27 wt.% Cu and 52 wt.% Mo contents. The chemical
analysis of the molybdenite concentrate matches with the company's analysis results
with 52 wt.% Mo content.
In this study, it was aimed to determine the optimum parameters for the total
oxidizing roasting process of molybdenite concentrate to produce MoO3 and purify
the MoO3 product by removing the copper content.
Present study was conducted in two main stages: First, MoS2 was roasted by
controlling parameters such as reaction temperature and duration in a chamber type
furnace. Before the roasting experiments, 20 grams of 18 samples were prepared and
put in a stove in order to dry the samples. To make a homogeneous roasting, alumina
boats which have large surface area, were used. The samples were put in the alumina boats as thin layers. Before the experiments, samples were weighted with the
alumina boats in order to calculate the weight losses.
Samples were roasted at 600 ºC, 625 ºC, 650 ºC with 15, 30, 45, 60, 90 and 120
minutes. The six samples which are in the same temperature set, were put in the
furnace. After starting the roasting process, samples were taken individually from the
furnace after respectively 15, 30, 45, 60, 90 and 120 minutes. Then the samples were
put in the desiccators for cooling. The highest Mo concentration rate was obtained as
56.6 wt.% of MoO3 at 650 °C for the roasting duration of 45 minutes.
In the second experimental sets, roasted product was leached by H2SO4 to remove
copper. Leaching conditions were optimized by investigating the effects of different
H2SO4 concentrations and S/L ratio.
Leaching experiments were done with Merck quality 95-98 % H2SO4 with the
duration of 15 minutes, at room temperature and 400 rpm mixing rate. All the
samples were 10 grams. During the leaching, acidic solution and powder samples
were mixed with a magnetic mixer. Leaching temperature was controlled by a
contact thermometer. After leaching, solid-liquid separation was done by a blue
banded filter. The solids were dried in a stove at 105 ºC for 12 hours.
In order to investigate the effects of different H2SO4 concentrations and S/L ratios ,
10 grams of samples were leached with 0.2 M, 0.4 M, 0.6 M acid concentrations with
1/5, 1/2 and 1/1 solid-liquid ratios. 97.7 wt.% of copper was removed by using 0.6 M
H2SO4 at 0.2 solid/liquid ratio.
The raw materials and the products were characterized by using AAS (atomic
absorption spectrometry) and XRD (X-Ray Diffraction) techniques.