0 Introduction

隨著社會經濟的飛速發展，我國對銅金屬的消費需求不斷增長，銅冶煉廠也不斷增加，且建設規模不斷增大。銅爐渣作為銅冶煉過程中產生的固體廢棄物，每年我國冶煉企業新增銅爐渣量達１０００萬ｔ左右，并呈現逐年遞增趨勢。銅爐渣的簡單堆存占用土地、污染周邊環境。因銅渣中仍然含有一定量的銅金屬，也造成資源的浪費。中國屬于銅礦石短缺國家，對于銅爐渣中有價金屬的綜合回收，有著重要的意義。目前國內外的銅冶煉企業都配套有對應的爐渣綜合回收系統，用于回收銅爐渣中的銅、鐵等有價金屬，同時最終尾礦可作為建筑材料外售給水泥廠等企業。對于銅爐渣選別系統回收的銅精礦，需要與冶煉廠外購的銅精粉混合后返回至熔煉系統，因此對銅精礦中的水分有一定的要求。這要求采用合適的脫水工藝，保證銅精礦中的水分能夠滿足冶煉要求。由于爐渣選別的銅精礦粒度相對較細，過濾脫水有一定的難度。以往大多數都采用陶瓷過濾機，其濾餅含水一般在１２％～１８％之間，水分較高。廣西某銅冶煉廠的銅精礦脫水工序采用板框式壓濾機，將水分控制在１０％左右，滿足了下游冶煉工藝的要求。

1Plate and frame filter pressesThe working principle of plate and frame filter press is a kind of intermittent solid-liquid separation equipment, which is composed of filter plates and frames arranged to form filter chambers, and under the pressure of feed pump, the slurry will be sent into each filter chamber, and the solids and liquids will be separated through filter media, which is characterised by simple structure, high pressure, and low water content of filter cake. The mechanism of plate and frame filter press is shown in Figure 1.

Plate and frame filter press realises the filtration and dewatering of slurry through the processes of filter plate pressing, slurry pump feeding, pressing and dewatering, blowing and dewatering, pulling off the filter plate and discharging. Its main working principle is as follows:

(1) Before feeding, the hydraulic station is started, and the hydraulic cylinder tightens the filter plate of the filter press, so that the filter plates are stacked on top of each other to form a closed filtering studio; the slurry pump transports the slurry to each filtering studio (the feeding pressure is about 0.8MPa), and the pressure of the slurry pump causes the filtrate to be discharged through the filtering cloth; the solid particles are retained by the filtering cloth to form the filter cake. When the filter cake reaches the appropriate thickness, stop feeding.

(2) Open the compressed air valve, the compressed air into the filter studio, high-pressure gas uniformly squeeze saturated filter cake, particle gap gradually reduced, the excess filtrate within the cake through the filter cloth outside.

(3) After pressing and dewatering, continue to introduce compressed air into each filtering studio (0.6~0.8MPa), the high pressure strong wind through the filter cake and filter cloth will bring out the residual water in the filter cake and blow dry the filter cake.

(4) After the dewatering process is completed, the automatic plate pulling device will pull open each filter plate in turn, and the filter cake between the plates will be discharged by its own weight, completing a filtration cycle.

2 Performance characteristics of plate and frame filter press Plate and frame filter press has the following characteristics compared with ceramic filter and vertical filter press:

(1) Compared with ceramic filter, the moisture content of filter cake is low. Plate and frame filter press through the feed squeeze, press and blow-dry three-stage filtration process, can significantly reduce the water content of the cake, especially for the specific gravity of the larger, finer particle size of the slag separation of copper concentrates, the filtered moisture can basically be controlled at about 10%, the filtration effect is significantly better than the ceramic filter.

(2) Although the water content of the cake of the plate and frame filter press and vertical filter press are both about 10%, the plate and frame filter press has the following advantages compared with the vertical filter press: fewer auxiliary equipments are required; the filter plate is placed vertically, and the replacement of the filter cloth is convenient and quick; the equipment has a low failure rate, and it is easy to operate.

(3) Filter press plate pressing, slurry pump feeding, pressing dewatering, blowing dewatering, pulling off the filter plate discharge and other processes are centrally controlled by PLC operating system, with a high degree of automation, which can achieve automatic operation without manual intervention and reduce the labour intensity of workers.

3 Problems that should be paid attention to in the production process Because the plate and frame filter press is intermittent operation equipment, the daily operation and maintenance is especially critical, in the use of equipment, improper use will not only affect the long-term stable operation of the equipment, but also affect the water content of the filter cake. In the production process, the following issues should be noted:

(1) slurry through the slurry pump feed to the filter press before, it is best to set a layer of grille screen, to prevent large particles or debris into the filter press, so as to avoid the feed channel blockage caused by the uneven force of the filter plate cavity stagnant bias broken plate, filter cloth by the sharp particles caused by the scouring of the breakage of the situation;

(2) The front end of the feed should be equipped with a certain volume of stirring tank, through continuous stirring to ensure that the concentration difference between the upper and lower layers of the slurry is less than 5%, and the stable feeding can ensure the formation of coarse and fine filter cake inside the filter chamber, which is convenient for the unloading of the filter cake and does not stick to the filter cloth;

(3) During the production process, regularly clean up the accumulation of material on the sealing surface under the filter plate to avoid slurry spraying and air leakage caused by the poor sealing of the filter plate due to the clamping of material on the sealing surface.

4 Summary in the smelter of copper slag sorting system construction of the early stage, generally the second stage of copper concentrate dewatering using ceramic filter, but the filtered copper concentrate moisture are higher, can not smelting process requirements, while the transport is also a certain degree of difficulty. With the emergence of vertical filter press, ceramic filter is gradually eliminated. Vertical filter press filtration effect is good, low water content of the cake, can meet the requirements of the smelting process, but this filter press due to more supporting equipment, so the failure rate is higher, operation, maintenance are relatively large workload. In the slag sorting system of a smelter in Guangxi, the plate and frame filter press was first used for two-stage dewatering, achieving a cake water content of about 10%, which not only meets the requirements of the smelting process and transportation, but also reduces the downtime of the equipment, reduces the labour intensity of workers, and opens up a new path for the future slag sorting system for the dewatering process of copper concentrates.

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