Roasters, gases from

In addition, the by-product (sodium sulfite) could cause problems if the simplified version of the flowsheet were to be adopted. In addition, the recycle of sodium sulfite to the roaster may contribute to the build-up of accretions in the roaster and in the boiler. Also, operating problems that could be experienced at higher rates could be blamed on this recycle whether or not it was the underlying cause of the operating problems. Direct incorporation of this material into the leaching plant could generate SO2 gas from tanks and launders. This could result from incomplete oxidation of the sulphites to sulphates. The use of a dedicated oxidation tower, or of an acid decomposition stage, represented an extra step and an additional capital expenditure. 

Three roasters operate in parallel to produce calcine. There are two 84-m fluidized bed roasters and a suspension roaster. Off-gas from the roasters is mixed with off-gas from the KIVCET furnace and is then processed in the sulphur gas handling area. By-products include calomel, sulphuric acid, liquid sulphur dioxide, and ammonium sulphate fertilizers. 

When an expanded production is considered, we have to treat more concentrate in the roasters. This leads to the generation of more process gas. From the view point of acid production capacity, the bottle necks were 1) insufficient capacity of the gas handling equipment, such as the air blowers, waste gas fans and gas blowers in the roasting process, 2) imbalance of heat in the roaster caused by increasing feed. 

This system consisted of low volume, high acidity streams such as the magnesium bleed electrolyte from the cellhouse and the Venturi scrubber water from the roaster gas cleaning operation. Typical compositions of these two streams are shown in Table I. 

Zinc concentrates contain various levels of selenium. Part of this selenium is released in the off-gas from the roasting operation. Following treatment of the roaster off-gas at an acid plant, the ultimate fate of the selenium is the weak acid effluent from the acid plant. 

As the sulfide ores (pyrites) are roasted, the roaster gas and the metal oxides produced are separated from each other in cyclones. 

Source Imported pastel Including from Mo roaster gas Liquid... 

The ore is ordinarily ground to pass through a ca 1.2-mm (14-mesh) screen, mixed with 8—10 wt % NaCl and other reactants that may be needed, and roasted under oxidising conditions in a multiple-hearth furnace or rotary kiln at 800—850°C for 1—2 h. Temperature control is critical because conversion of vanadium to vanadates slows markedly at ca 800°C, and the formation of Hquid phases at ca 850°C interferes with access of air to the mineral particles. During roasting, a reaction of sodium chloride with hydrous siUcates, which often are present in the ore feed, yields HCl gas. This is scmbbed from the roaster off-gas and neutralized for pollution control, or used in acid-leaching processes at the mill site. 

Typical applications in the chemical field (Beaver, op. cit.) include detarring of manufactured gas, removal of acid mist and impurities in contact sulfuric acid plants, recovery of phosphoric acid mists, removal of dusts in gases from roasters, sintering machines, calciners, cement and lime Idlns, blast furnaces, carbon-black furnaces, regenerators on fluid-catalyst units, chemical-recoveiy furnaces in soda and sulfate pulp mills, and gypsum kettles. Figure 17-74 shows a vertical-flow steel-plate-type precipitator similar to a type used for catalyst-dust collection in certain fluid-catalyst plants. 

The development of electrostatic precipitators soon led to new applications, including the separation of metal oxide fumes. This was followed by various metal manufacturing processes such as the lead blast furnace, ore roaster, and reverberatory furnace. Electrostatic gas cleaning was soon applied also in cement kilns and in several exotic applications, such as recovering valuable metals from exhaust gases. 

Flydrochloric acid regeneration. This process is used to treat the spent pickle liquor containing free hydrochloric acid, ferrous chloride, and water that is obtained from steel finishing operations. The liquor is concentrated by heating to remove some of the water, followed by thermal decomposition in a roaster at temperatures (925 to 1050°C) sufficient for complete evaporation of water and decomposition of ferrous chloride into iron oxide (ferric oxide, Fe203) and hydrogen chloride (HC1) gas.19 The iron oxide is separated for offsite recovery or... 

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