Zinc residue treatment process

At the same time, changes were introduced in the feed residues from the electrolytic zinc plant are processed with some addition of zinc-bearing materials from the waste water treatment plant, and other secondaries like EAF dusts coming from steel mills (electric arc... 

C. Mattich, K. Hasselwander, H. Lommert and A.N. Beyzavi, Electrolytic Zinc Manufacture with Waelz Treatment of Neutral Leach Residues , Zinc and Lead Processing. J.E. Dutrizac, J.A. Gonzalez, G.L. Bolton and P. Hancock, Eds., Canadian Institute of Mining, Metallurgy and Petroleum, Montreal, Canada, 1998, 561-578. 

Precipitation can also occur upon chemical reaction between the impurity and a precipitating agent to form a compound insoluble in the molten metal. The refining of cmde lead is an example of this process. Most copper is removed as a copper dross upon cooling of the molten metal, but the removal of the residual copper is achieved by adding sulfur to precipitate copper sulfide. The precious metals are separated by adding zinc to Hquid lead to form soHd intermetaHic compounds of zinc with gold and silver (Parkes process). The precious metals can then be recovered by further treatment (see Lead). 

Splash condenser dross residue. The treatment of steel production pollution control sludge generates a zinc-laden residue, called dross. This material, generated from a splash condenser in a high-temperature metal recovery process, is known as a splash condenser dross residue. Because this material contains 50 to 60% zinc, it is often reclaimed, reused, or processed as a valuable recyclable material. Facilities commonly handle this material as a valuable commodity by managing it in a way that is protective of human health and the environment, so U.S. EPA excluded this residue from the definition of solid waste. 

DEZ [Diethyl zinc] A process for preserving books and documents by treatment with diethyl zinc vapor, which neutralizes ary residual acidity from the papermaking process. The articles are placed in a low-pressure chamber and suffused by diethyl zinc vapor. This vapor reacts with the moisture in the paper to yield zinc oxide, which neutralizes the acid. The process was developed by Texas Alkyls (a joint company of Akzo and Hercules) and the U S. Library of Congress. A pilot plant was set up in 1988, capable of treating batches of 300 books, and plans to build two larger plants were announced in 1989. 

The zinc sulphate produced in this process can be turned more easily to commercial account than iron sulphate. If to the solution of the zinc sulphate resulting from the process sodium carbonate or sodium hydrogen carbonate is added, a precipitate of hydrated zinc basic carbonate or zinc carbonate is obtained, which on ignition in a furnace yidds zinc oxide (commercially known as zinc white ), water, and carbon dioxide. Zinc white has a commercial value as a basis or body In paints it has one great advantage over white lead, which is used for the same purpose, in that it is far less poisonous. This method of treatment of the residual... 

Indium may be recovered from zinc ores by several patented processes. Usually it is recovered from residues obtained from zinc extraction. The residues, slags, fume, or dusts from zinc smelting or lead-zinc smelting are treated with a mineral acid. Other steps involved in recovery often vary, but mostly use solvent extraction and precipitation steps. In some processes, treatment with caustic soda yields indium hydroxide. The hydroxide is calcined to obtain oxide, which then is reduced with hydrogen at elevated temperatures to obtain the metal. Distillation or electrolysis are the final steps to... 

In another industrial process, flue dusts from smelting lead and zinc concentrates are boiled in acidified water. Thallium dissolves and is separated from insoluble residues by filtration. Dissolved thallium in solution then is precipitated with zinc. Thallium is extracted from the precipitate by treatment with dilute sulfuric acid which dissolves the metal. The solution may also contain zinc, cadmium, lead, copper, indium, and other impurities in trace amounts. These metals are precipitated with hydrogen sulfide. The pure thallium sulfate solution then is electrolyzed to yield thallium. 

Sulfite paper has a relatively short life span, since residual acid will continue to hydrolyze the cellulose and cause embrittlement. Further sources of acid include aluminum sulfate (which is added together with resin to suppress bleeding or feathering of ink into the paper) and S02 and NO from the atmosphere. Much of the world s library collections and archives will soon be lost as the paper crumbles. Various deacidification treatments (e.g., with ammonia, morpholine, cyclohexylamine carbamate, or diethyl-zinc) have been proposed and tried, but at best they can only halt the process of embrittlement and cannot reverse it.14 With the move to kraft pulping, alkaline peroxide bleaching, and increasing use of precipitated calcium carbonate as a filler, the high quality papers produced today are intrinsically acid free and should also resist subsequent acidification by S02-polluted air fairly well. 

The assay of gold ores can be effected by heating with litharge on a cupel, which absorbs the molten lead oxide and dissolves impurities. The residual metallic button is then alloyed with silver, and parted by means of nitric acid. Zinc 6 and cadmium 6 can be substituted for the silver in this process. Any platinum present is dissolved by repeated alloying and treatment with nitric acid.7... 

Full processes for the preparation of aromatic isocyanates by DMC were also patented. In particular recently it was published a patent which claims an integrated process for the production of aromatic isocyanates without phosgene. In the examples the various phases of the process are repotted, starting form the reaction of the amine (TDA) with DMC to carbamate with zinc acetate dihydrate as catalyst, following a passivation treatment of the urethane catalytic residues and then pyrolysis of urethane in gas phase. 

Figure 3-7 Comparison of Zinc-"Pools" in A Sample of Heat Processing Residues Before and After Treatment with pH 5/400 mV Solutions (AC = Ammonium Acetate OX = Oxalate Buffer Solution HP = Peroxide-Extraction NA = Residual Fraction)...

Four process streams closely link the zinc and lead operations. Iron and lead residues produced in Ae zinc operation are treated in the lead operation, and comprise nearly half of the total feed to the lead operation. Zinc-rich smelter fume makes up about 15% of the total feed to the zinc operation. Lead smelter sulphur dioxide off-gases are fed to the sulphur gas handling plants in the zinc operation, and waste water streams from both lead and zinc operations are treated in the effluent treatment plant. 

In the course of increasing the production ctq>acity of zinc at the Onsan Refinery from 50,000 tons per year in 1978, the first year of operation, to 350,000 tons per year in 1999, the treatment of iron-containing residue, which is currently a goethite residue, has been an important issue because of the limited space at the plant. Korea Zinc investigated the available technologies for a process that could produce an inert material and meet the limits of the pollution restrictions. The requirements for the new process installed at Korea Zinc were as follows ... 

T.T. Chen and J.E. Dutrizac, Mineralogical Study of Jarofix Products for the Stabilization of Zinc Industry Jarosite Residues , Second International Symposium on Extraction and Processing for the Treatment and Minimization of Wastes . V. Ramachandran and C.C. Nesbitt, Eds., The Minerals, Metals and Materials Society, Warrendale, PA, U.S.A., 1996,659-672. 

The first production step is pyrometallurgical treatment of leach residues or roasting products from zinc ore processing. The impure zinc oxide is reduced with coke or carbon monoxide. In this process, germanium, cadmium, indium and thallium, which usually follow zinc, are reduced to the metallic state. They vaporize and are separated by fractional condensation. The germanium fraction is transformed to the tetrachloride by treatment with hydrochloric add. 

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