METAL MINING TECHNOLOGY IN JAPAN

Transcription

1 METALMINING TECHNOLOGY IN JAPAN

2 Foreword The Ministry of International Trade and Industry(MITI),the Government of Japan, decided to make Mining Expert Training materials for technical cooperation program in the fi scal year And MITI entrusted its execution to the Metal Mining Agency of Japan (MMAJ). This text, in combination with pictures (video tape and slides),was planned by MMAJ, and produced by Dowa Mining Co., Ltd.(Dowa).Without permission of JOGMEC, any copying and use other than for the purpose of Mining Expert Training are strictly prohibited. 1. At Beginning The history of mineral processing technology for Kuroko, a typical complex sulfi de ore. in Japan, took place at the Kosaka and Hanaoka Mines. Todayʼs processes were established after numerous improvements and the development of SO2-lime and hot pulp fl otation. This text will briefl y describe the mineral processing technologies of Kuroko using the Matsumine Mill at Hanaoka Mine in Akita Prefecture. 2. Kuroko The Kuroko consists of a dense, complex mixture of valuable minerals such as sphalerite, galena, chalcopyrite, pyrite and borite, and in lesser proportions, bornite, chalcocite and tetrahedrite. It also contains rare metals like gallium, indium and bismuth. Gangue minerals are quartz, gypsum and clay. Table 1 Throughput and head grade at Matsumine Mill *Sulfer in Pyrite crushing plant, grinding and fl otation plant, reagent and boiler house, and fi ltration plant Crushing Process 3. Matsumine Mill 3-1. Outline Gathering and mixture 40,000 tons of minerals per month from the Matsumine, Fukasawa and Ezuri Mines, the Matsumine Mill treats the ore to produce concentrates of copper, lead, zinc, pyrite and barite, The head grades are 1g/ton for Au, 100g/ton for Ag, 2% for Cu, 2% for Pb, 8% for Zn, 10% for Py-S and 10% for BaSO 4. The amounts treated and head grades are listed in Table 1. The plant consists of a stockyard and four independent facilities: Minerals from Fukasawa and Ezuri Mines are transported by truck to the stockyard and fed to the crushing plant. Minerals from Matsumin Mine are lifted up with a skip and fed to the crushing plant via the stockyard. The crushing plant includes water washing, coarse ore crushing, and sand slime classifi cation processes, with a 200 t/h processing capacity. Ore smaller than 100 mm produced by the primary crusher at each mine is washed by a drum washer and screened with vibrating screens. Coarse ore is crushed with gyratory and cone crushers down to 25 mm.

3 In the sand slime classifi cation process, the washed ore from the drum washer is classifi ed by spiral classifi ers and cyclones, and the slime is fed to a slime thickener, while the sand is dewatered with an extractor, conveyed to ore bins together with crushed products of coarse ore, and then stored in bins labelled according to the mine of origin Grinding Process Grinding includes a 3 stage grinding process consisting of a rod mill in an open circuit and two ball mills in a closed circuit with cyclones. Minerals obtained from ore bins of Matsumine, Fukasawa and Ezuri Mines are blended, and then a given quantity of the mixture is fed into the rod mill. The ground product is of 70%-200 mesh grain size, which is then sent to the fl otation process 3-4. Flotation Process (1) Diffi culties with Flotation of Kuroko The Flotation of Kuroko is diffi cult for the following reasons. It is very diffi cult to obtain the liberation of minerals from Kuroko because of its fi ne grained texture. In general, Kuroko is easily oxidized, so that its mineral face becomes contaminated and deteriorates. This phenomena prevents Kuroko from showing fl otation behavior normally inherent in minerals. Kuroko contains large volumes of many kinds of useful minerals. Kuroko also contains large volume of various kinds of clay minerals as gangue. (2) History of Flotation at Kuroko Todayʼs process for fl otation at Kuroko was established after various improvements. Around 1970, as shown in Fig. 1, fl oats of copper, lead and zinc were obtained by bulk fl otation based on the high-lime process. From here the lead fl oat was separated by sodium cyanide, and sinks were fi ltrated, and heaped and divided into fl oat of zinc and sink of copper by hot pulp fl otation. Furthermore, concentrate of pyrite was obtained by G: gangue Fig. 1 Flowsheet of high lime process at Matsumine Mill

4 pyrite fl otation from the tailings of the bulk fl otation of copper, lead and zinc. Results of this mineral processing are shown in Table 2, and both grades and recoveries were far beyond satisfaction. The current fl ow sheet is shown in Fig. 2. First, after conditioning with sulfur dioxide and hydrated lime, fl oats of copper and lead are obtained by semi-bulk fl otation. Bulk concentrates of copper and lead are separated into a fl oat of copper and a sink of lead by hot pulp fl otation. After the semi-bulk fl otation Table 2 Metallurgical results of high lime process (1970) Table 3 Metallurgical Results of SO2-lime Process (1985) Fig. 2 Flowsheet of So2-lime process at Matsumine Mill

5 of copper and lead, fl oats of zinc, pyrite and barite are obtained by differential fl otation to produce respective concentrates. The slime is sent to silver fl otation, and the fl oat is put into the copper and lead semi-bulk fl otation circuit. Results of the present process are shown in Table 3, and both grades and recoveries have been dramatically improved. Practical operations are described below. (3) Semi-bulk Flotation of Copper and Lead The semi-bulk fl otation process of copper and lead consists of conditioning with sulfur dioxide to ph4.5 and with hydrated lime to ph5.5, plus addition of a collector of dithiophosphates. Semibulk fl otation is conducted to the tertiary cleaning stage and concentrates are fed into the copper-lead separation fl otation. The depressant action of sulfur dioxide in the semi-bulk fl otation can be understood in the following way. The addition of sulfur dioxide forms sulfi tes on the surfaces of sphalerite and pyrite, preventing adsorption of the collector which, however, can be adsorbed to the surfaces of chalcopyrite and galena. As a result, sphalerite and pyrite are not fl oated by contact with air bubbles because of their hydrophilic surfaces. (4) Copper-Lead Separation Flotation With copper-lead separation fl otation, copper is obtained as fl oats, and lead sinks by warming the conditioner to 6070 through direct introduction of steam. This process has been developed to replace the conventional process using sodium cyanide, and has brought great productivity increases, while solving environmental problems due to sodium cyanide. It has also eliminated dissolution problems of gold and silver. The separation of chalcopyrite and galena in the hot pulp fl otation can be understood in such a way that when the pulp is warmed to at

6 METAL MINING TECHNOLOGY IN JAPAN1 MINERAL PROCESSING OF COMPLEX SULFIDE OREKUROKO