Sülfatlı çözeltilerden bakır ve kobaltın H2S ile çöktürülme kinetiğinin incelenmesi
The Investigation of precipitation kinetics of copper and cobalt by H2S in sulphate based solutions
- Tez No: 21962
- Danışmanlar: DOÇ. DR. ERCAN AÇMA
- Tez Türü: Yüksek Lisans
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1992
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 89
Özet
Bu tez çalışmasında, sülfatlı çözeltilerden bakır ve kobaltın, hLS gazı ile sülfür olarak çöktürülme ki netiği incelenmiştir. Bu amaçla CuS çöktürülmesinde pH, gaz debisi, gaz kabarcık çapı ve başlangıç çözelti konsantrasyonun etkisi incelenmiştir. CoS çöktürülme sinde ise yukarıdaki parametrelere ilave olarak sıcaklı ğın etkisi de ölçülmüştür. Bu tez kapsamında yapılan deneylerden elde edilen önemli sonuçlar şu şekilde sıralanabilir. 1)- Sülfatlı çözeltilerden Cu ve Co ' in H?S gazının çözeltiden gaz kabarcıkları şeklinde geçirilerek, sülfür halinde çöktürülmesi, heterojen bir reaksiyon olup, çök me kinetiği Higbie teorisi ile açıklanabiLmektedir. 2)- Çözelti pH'sının yükseltilmesi çökme hızlarını arttırmaktadır. 3)- Sıcaklığın azalmasıyla, çökme hızları düşmek tedir. 4)- Gaz debisinin artması ve gaz kabarcık çapının azalmasıyla kütle transfer katsayıları artmakta, dolayı sıyla çökme reaksiyonu hızlanmaktadır. 5)- Başlangıç çözelti konsantrasyonun artması, çökme hızını etkilememesine rağmen, çökme süreleri art maktadır.
Özet (Çeviri)
The aim of this study is to investigate the precipitation kinetics af CüS and CoS from sulphate-based.solutions' by H?S.“The parameters were pH, gas flow rate, gas bubble diameter, and initial solution concentration in CuS precipitation experiments. The effect of temperature was used as an additional parameter in CoS precipitation experiments. The ability of hydrogen sulphide to precipitate, a rather impressive list of metals from aqueous solution has been a part of the analytical chemistry. It is only in recent years that hydrogen sulphide has been realized as â potential reagent for number of large scale hydrometallurgical processing. In the past, H?S has suffered from three serious disadvantages to its commerical use, which are: 1)- It is expensive, 2)- It is both toxic and inflammable, 3)- Its aqueous solutions are corrosive, Modern developments have changed this situation. It is possible to generate H”S at high purity by reacting hydrogen with sulphur vapor. The development of apparatus,, to do this efficiently now qualifies M?S as a cheap tonnage chemical. Further, the old objections theuse of H“S because of its-hazardous properties appear VIto be largely subjective. If its dangers are recognized and safety precautions are taken, H”5 is no more dangerous than propane, chlorine, oxygen or ammonia. Finally,“the continuing development of corrosion-resistant construction materials have reduced the problem of equipment maintenance due to the corrosive nature of H”S bearing solutions to the varishing paint. The precipitation of metal sulphides by..,gaseous hydrogen sulphide have been utilized as a method in the solution purification or the production of bulk sulphide concentrates from dilute leach liquors. The most common practice in industrial applications is the precipitation of metals, either for selective or bulk precipitation methods sulphide concentrates fronf- coloured metal ion solutions. The Outokumpu Mine, in Finland, produces about 150.000- 200.000 tons annually pyrite-pyrrhotite flotation concentrate, which contains cobalt, nickel, copper and zinc. The sulfur in this concentrate has been in demand by the domestic paper and pulp industry and also for the sulfuric acid production for a long time. Calcine and green concentrate are being sulfatized“in fluid bed roasters. After ttresulf atizing roasting, the soluble metals are being leached, yielding a pregnant solution, from which copper, zinc, nickel + cobalt precipitated selectively by H”S, and leaving an iron oxide residue (purple ore). The Sherritt-Gardon ammonia leach process for the treatment of nickel-rich concentrates makes the use of H?S in - early stage to complete the removal of copper from the the leach solution. Later in the process, after the reductive precipitation of the majority of the nickel by hydrogen, the cobalt and remaining nickel are stripped from solution as sulphides. Other processes developed by Sherritt also use metal sulphide precipita tion such as the Laterite and Matte leach processes, and the Sherritt-Cominco copper process.In the Mao-Bay plant, lateritic iron ores of Cuba are being leached with sulfuric acid under pressure»In the second phase, a high grade concentration can be obtained from the dilute liquor, after the precipitation of Ni, Co, Fe, Al, Cr, Cu, Zn, and Pb by H“S. The sulfide slürr-y- is then treated in agitated in pressurized vessels by oxidizing the sulfide solids to sulfates. The liquor from this step is purified in two steps: by adjusting the pH to 5-5.5 with ammonia and aerating it, iron, aluminum, and chromium are precipitated as hydrous oxides and filtered off. The pH is then adjusted with acid to about 1. 5, and ?then copper,, lead, and zinc precipitated with hydrogen sulfide. ions The reaction of bivalent metal ions with sulphide 2 + 2- M + S = FIS is a homogeneous reaction confirming to normal second- order chemical kinetics. However, the basic reagent is a gas. hydrogen sulphide, and the overall reaction. H + H2S = MS + 2H + involves several stages. Since the reaction involves in between gas and liguid ions, the reaction confirmes a first order chemical kinetics. These are summarized as follows : ; -.- 1)- Transfer of H”S from the gaseous phase and dissolution in -the aqueous phase, H2S(g) = H2S,, M (aq) 2)- Dissociation of H“S to give sulphide iom a- H”S, x = HS“ + H+ 2 (aq) b- HS”_ 52- + H“ V1X13)- Reaction between proper sulphide anions and metal cations But, these stages are only valid in homogeneous reactions. Actually, the precipitation of metal sulphide by bubbling hydrogen sulphide through a solution is a typical gas- liquid interface reaction, and takes place in the following steps : 1)- Absorption of hydrogen sulphide at the gas- solution interface, 2)- Diffusion of hydrogen sulphide to the reaction zone, 3)- Diffusion of metal cations to the reaction zone, k)- Chemical reaction at the reaction zone, 5)- Diffusion and precipitation of reaction products away from the reaction zone. As the absorption and chemical reaction steps are generally known to be much faster than the diffusion steps therefore steps 2 and 3 control the overall reaction rate and the reaction rates can be calculated by utilizing the methods explained in Higbie Theory. The results of this study have shown that: 1)- The precipitation kinetics of copper with H”S from sulphate solutions has been explained in Higbie Theory. The three steps of cobalt precipitation are nucleation, chemical reaction at the gas-liquid interface, and homogeneous precipitation. Only the second step can be explained by Higbie Theory, and other kinetic models may be used in explanation of the other two steps. 2)- In order to precipitate CoS during the experiments, it was necessary to saturate the salûticn with H“S gas, and then adding one or two drops of NH, ' IXto solution, which causes the increase in pH in very limited area, resulting the formation of CoS particulates that initilazes the CoS precipitation. 3)- It was found that an increase in pH also increased. the precipitation rates of copper and cobalt due to the Increase of- the sulphur ion concentration in the solution..Copper can be precipitated- '-in, a. -.wide range, of pH. Since the solubility value o,f^ CuS_ is so'- small thai: there- is. a thermodynamic tendency for its^pre-cipitati.on ”at -any - given pH, whereas cobalt can be vprecipatated-by using 'CoS particules. as a catalyst, if pH' is greater than-2.0..-?..' However, for the. selective precipitation, pH should be selected carefully- because of the contamination problem. k)- In CoS precipitation, the precipitation reaction rates decreased with an increase in temperature due to the decrease of the hydrogen sulphide solubility. However, an increase in temperature also increases the thermodynamic tendency of metal sulphide precipitation. 5)- An increase in gas flow rate or a decrease in gas bubble diameter increases the precipitation reaction rate due to the increase in the mass transfer coefficient, 6)- An increase in the initial solution concentra tions does not affect the precipitation reaction rate, but an increase in the precipitation time can be correlated higher H“S concentration in solutions due to an increase of the required H”S concentration in solution. 7)- The calculated mass transfer coefficients, in this study can be used in- design of reactors.
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