MMK28403 Metal Extraction Technology PDF

PYROMETALLURGY DR MEOR AHMAD FARIS MEOR AHMAD TAJUDIN FACULTY OF MECHANICAL ENGINEERING & TECHNOLOGY MMK28403 – METAL EXTRACTION TECHNOLOGY  INTRODUCTION  Pyrometallurgy is a branch of metallurgy where heat is the principle means of extracting metals from ores or o...

PYROMETALLURGY DR MEOR AHMAD FARIS MEOR AHMAD TAJUDIN FACULTY OF MECHANICAL ENGINEERING & TECHNOLOGY MMK28403 – METAL EXTRACTION TECHNOLOGY  INTRODUCTION  Pyrometallurgy is a branch of metallurgy where heat is the principle means of extracting metals from ores or other materials.  Pyrometallurgic techniques include: ► ore-dressing ► Sintering ► Roasting ► Calcination ► smelting ► refining.  Normally, the final product is in the molten form. Ore-dressing is the preparation of ore using crushing, grinding, washing, drying, flotation, etc. Roasting is a process in metallurgy in which a sulfide ore is heated in air. The process may convert a metal sulfide to a metal oxide or to a free metal.  Calcinations is the process to decompose the carbonates and other compounds, causing loss of moisture, reduction or oxidation using a high temperature but below the melting or fusing point.  Sintering is the process which produces agglomerated fine powders.  Smelting is a chemical process to isolate an element from its ore using heat and a reduction agent.  Refining consists of purifying an impure material. TYPICAL FLOWCHART COPPER  TYPICAL FLOWCHART IRON  TYPICAL FLOWCHART ZINC  REACTOR DESIGN A metallurgical reactor is defined as a piece of equipment designed to carry out a certain type of reaction and or a certain unit process.  DRYING Materials containing water are often encountered at various stages in the conversion processes of ore to metal. Examples include ores, concentrates and compound intermediates.  Some of the reasons for water removal prior to further processing are :-  The elimination of water reduces the weight of the material handled.  If the material is to be charged in an electric furnace where the operating temperature is high (~1700 °C), the sudden release of water can cause charge blow off.  The material becomes more reactive following water removal.  The presence of water can cause undesirable side reactions which leads to poor product quality and yield.  Water presents in the materials of interest as free water or water of crystallization or combined water. The process of dehydration refers to the removal of the water of crystallization while the removal of water is called dehydroxylation because hydroxyl groups in the material are broken down to form water vapor. The dehydroxylation process is very often alternately described as calcination.  Drying usually accomplished by passing hot combustion gases through or above the substance. May be carried out in a number of different types of furnaces, e.g., in a rotary kiln or fixed or fluidized bed. Since the temperature is relatively low, there are usually no serious material problems.  CALCINATION The term calcination is used to denote thermal decomposition of solids and is expressed by the general reaction as follows :- Solid 1 = Solid 2 + Gas Calcination is a widely used unit operation in process metallurgy and the compound represented as solid 1 is usually a carbonate and solid 2 an oxide. The decomposition of hydroxides besides termed as drying is also called calcination. Example : CaCO3 (s)= CaO (s) + CO2 (g) Calcination is more endothermic than drying. Thus, for the reaction CaCO3 = CaO + CO2, ∆H298 = 177.8 kJ and the heat must be supplied at a relatively high temperature. Objectives of calcination are mainly to bring thermal decomposition, phase transition, removal of volatile fractions such as CO2, H2O.  The rate of calcination is governed primarily by the supply of the necessary heat of decomposition. Three different types of furnaces are generally in use for calcination:- ► The shaft furnace is considered to be the most suited for calcining coarse limestone. ► Furnaces of the rotary kiln type are used for handling materials of mixed particle sizes and lumps which disintegrate during the process. ► Calcination can be carried out in a fluidized bed- reactor for materials of small and uniform particle size. These furnaces are usually fired with gas, oil or coke. In some cases electric heating is resorted to.  Shaft Furnace Rotary Kiln Fluidized Bed Reactor  ROASTING Mostly used for sulfidic sources of metals. Roasting is the oxidation of metal sulfides to produce metal oxides and sulfur dioxide. Carried out by heating the sulfides in air or in oxygen. Usually carried out below the melting points of the sulfides and oxides involved, usually below 900 to 1000 °C.  Sulfide ore or concentrate is subjected to roasting in order to achieve one or more of the following objectives :-  partial oxidation causing loss of part of the sulfur content.  oxidation to sulfates which is essentially called sulfation roasting.  complete removal of sulfur, i.e. conversions to oxides which is essentially called dead roasting. The conditions to be used for achieving each of these objectives are different and are determined by the thermodynamic properties of the pertinent metal- sulfur-oxygen (M-S-O) systems.  Copper Extraction Chalcocite (Copper sulphide Cu2S) Chalcopyrite (Copper iron sulphide, Cuprite (Copper oxide, Cu2O) CuFeS2) Extraction process by PYROMETALLURGY Extraction process by For copper sulphide based ores HYDROMETALLURGY For copper oxide or carbonate based ores  SINTERING Sintering is process which produces agglomerated fine powders. It is based on atomic diffusion. Diffusion occurs in any materials above absolute zero (theoretical temperature at which entropy reaches its minimum value) but it occurs much faster at higher temperatures. The powdered materials is held in a mold and then heated to a temperature below the melting point. The atoms in the powder particles diffuse across the boundaries of the particles, fusing the particles together and creating a solid piece.  Sintering is effective when the process reduces the porosity and enhances other properties like strength, thermal conductivity etc. In any sintering process, the preparation of feed material is very important. Sintering – is the high temperature treatment that causes particles to join, gradually reducing the volume of pore space between them. Sintering – diffusion of atoms to points of contact causes bridges to form between the particles. Further diffusions eventually fills in any remaining voids. The driving force for sintering is a reduction of total surface area of the powder particles  The feed must have appropriate porosity, moisture content and metallurgical fuels to ensure that the sintered material has even physical and chemical properties. Roasting of sinter is the final process to remove the sulfur and evaporate elements like calcium or substances like Sb2O3. In many final roasting, sulfur is very hard to be removed. Examples in Pyrite treatment, to produce SO2 for sulfuric acid making, FeS2 is roasted and SO2 gas used as the feed for acid.