![\"\u9694\u819c\u538b\u6ee4\u673a\u4ece\u7535\u89e3\u950c\u6d78\u51fa\u6e23\u4e2d\u6d78\u51fa\u4e0e\u56de\u6536\u950c](\"https:\/\/www.xiaoxianmi.cn\/wp-content\/uploads\/2024\/07\/image-3.png\" "\\"\u9694\u819c\u538b\u6ee4\u673a\u4ece\u7535\u89e3\u950c\u6d78\u51fa\u6e23\u4e2d\u6d78\u51fa\u4e0e\u56de\u6536\u950c")
<\/p>\n1 Introduction<\/p>\n
Zinc sulfide ores are the main source of zmc metal in the world\uff0cin which zinc generally exists in forms of sphalerite and marmatite\uff0eCurrently,more than 80\uff05of the zinc is produced by conventional zinc hydrometallurgical methods\uff0cincluding roasting\uff0cleaching and electrowinning processes[1\uff0c2\u3011\uff0eDuring the roasting process\uff0cZnS is converted to ZnO\uff0cbut a significant fraction of ZnO reacts with the iron impurities to form zinc ferrite\u300e3\u201451\uff0eZinc ferrite is insoluble in mild acidic conditions\uff0c\u5f3aHs\uff0ea considerable amount of leaching residue will be produced in the subsequent leaching process f6\uff0c7]\uff0eIn addition\uff0cthe leaching reaction rate decreases over time due to the decreasing acid concentration during the tradifional leaching process in stirred tank\uff0eConsequently,incomplete leaching will OCCur,thereby further increasing the generation of zinc leaching residue(ZLR)\uff0cleading to a significant waste of resources and a high environmental risk\u30108\uff0c9\u3011\uff0e The high demand for zinc has attracted the interest of industry to utilize the ZLR as a valuable secondary source[1]\uff0eHydrometallurgical processes are dely applied to recycle zinc from ZLR due to their significant advantages of lower capital and operating costs\uff0cas well as being less harmful to the environment[1\uff0c2]\uff0eCurrently, the most common hydrometallurgical process is to recover zinc from ZLR in a bath of hot concentrated sulfuric acid\u300e10]\uff0eA high extraction rate of zinc can be obtained using this process\uff0cbut incomplete leaching still occurs due to the leaching in the stirred tank\uff0eMoreover, the hot concentrated acid leaching process involves a long reaction time f4\u20146\u00a8and consumes an enormous amount of energy and sulfuric acid to process the 1arge amount of ZLRs obtained by thickening\uff0e More importantly,in most electrolytic zinc plants\uff0cthe ZLRs containing water-soluble zinc with a content of less than 5\uff05are directly discharged or heaped\uff0ecausing a portion of the zinc losses\uff0eThe water-soluble zinc can cause soil contamination\uff0cwater pollution and several other serious environmental pollution through the leachate by rainfall[8\uff0c9]\uff0eTherefore\uff0cfinding a cost effective and environmental friendly process to recover zinc from ZLR remains a major challenge\uff0e The membrane filter press(MFP)\uff0ewhich is a common machine on solid\uff0e1iquid separation\uff0chas advantages of low cost\uff0chigh solid content and outstanding efficiency that has been widely used in various industries\uff0eIn recent years\uff0ethe washing functionof MFP has also been attracting attention for use in the titanium dioxide\uff0csugar,pigment and electrolytic manganese metal industries[1\u535c14]\uff0eLIU et al[14] recovered 50\uff05of water-soluble manganese from an electrolytic manganese residue fEMR)via a MFP using water\uff0eThis MFP\u2014based water washing technology could be industrially applied because it solves the problem of \u2018’water swelling\u201d\uff0ewhich commonly occurs in previous water washing technologies[1 4\uff0c1 5]\uff0eOn the basis of the previous work of LIU et al[1 4]\uff0cwe attempted to wash the EMR via a MFP using anolyte\uff0eIn 2009\uff0cthe MFP\u2014based technology on the leaching and recovery of manganese from EMR via a combination of anolyte washing with water washing was realized and resulted in a patent application being submitted(No\uff0eCN1 024700A) \u300e1 61\uff0eNote that several demonstrative operations have also been constructed in China based on this technology\uff0e However,the possibility of using this technology in the hydrometallurgical zinc process has never been investigated previously\uff0eIf this technology could be used in electrolytic zinc plants\uff0cthe thickening\uff0cpulping\uff0c second leaching\uff0cwashing\uff0cfiltering and pressing would be integrated and realized using a single MFR In addition\uff0cthe leaching of zinc from ZLR in the form of spent electrolyte washing would be performed under constant acid concentration via a continuous flow of spent electrolyte\uff0e Hence\uff0ethe feasibility of leaching and recovery of zinc from lcaching residue of zinc calcine based on MFP was investigated\uff0ccombining spent electrolyte washing with flesh water washing\uff0eFor this work\uff0ethe uniformity of filter cakes\uff0ewhich is directly related to the leaching result\uff0cwas examined\uff0eBased on this experimental result\uff0c the 1eaching and washing on extracting zinc from ZLR were subsequently studied\uff0e<\/p>\n
1 Introduction<\/p>\n
Zinc sulfide ores are the main source of zmc metal in the world\uff0cin which zinc generally exists in forms of sphalerite and marmatite\uff0eCurrently,more than 80\uff05of the zinc is produced by conventional zinc hydrometallurgical methods\uff0cincluding roasting\uff0cleaching and electrowinning processes[1\uff0c2\u3011\uff0eDuring the roasting process\uff0cZnS is converted to ZnO\uff0cbut a significant fraction of ZnO reacts with the iron impurities to form zinc ferrite\u300e3\u201451\uff0eZinc ferrite is insoluble in mild acidic conditions\uff0c\u5f3aHs\uff0ea considerable amount of leaching residue will be produced in the subsequent leaching process f6\uff0c7]\uff0eIn addition\uff0cthe leaching reaction rate decreases over time due to the decreasing acid concentration during the tradifional leaching process in stirred tank\uff0eConsequently,incomplete leaching will OCCur,thereby further increasing the generation of zinc leaching residue(ZLR)\uff0cleading to a significant waste of resources and a high environmental risk\u30108\uff0c9\u3011\uff0e The high demand for zinc has attracted the interest of industry to utilize the ZLR as a valuable secondary source[1]\uff0eHydrometallurgical processes are dely applied to recycle zinc from ZLR due to their significant advantages of lower capital and operating costs\uff0cas well as being less harmful to the environment[1\uff0c2]\uff0eCurrently, the most common hydrometallurgical process is to recover zinc from ZLR in a bath of hot concentrated sulfuric acid\u300e10]\uff0eA high extraction rate of zinc can be obtained using this process\uff0cbut incomplete leaching still occurs due to the leaching in the stirred tank\uff0eMoreover, the hot concentrated acid leaching process involves a long reaction time f4\u20146\u00a8and consumes an enormous amount of energy and sulfuric acid to process the 1arge amount of ZLRs obtained by thickening\uff0e More importantly,in most electrolytic zinc plants\uff0cthe ZLRs containing water-soluble zinc with a content of less than 5\uff05are directly discharged or heaped\uff0ecausing a portion of the zinc losses\uff0eThe water-soluble zinc can cause soil contamination\uff0cwater pollution and several other serious environmental pollution through the leachate by rainfall[8\uff0c9]\uff0eTherefore\uff0cfinding a cost effective and environmental friendly process to recover zinc from ZLR remains a major challenge\uff0e The membrane filter press(MFP)\uff0ewhich is a common machine on solid\uff0e1iquid separation\uff0chas advantages of low cost\uff0chigh solid content and outstanding efficiency that has been widely used in various industries\uff0eIn recent years\uff0ethe washing functionof MFP has also been attracting attention for use in the titanium dioxide\uff0csugar,pigment and electrolytic manganese metal industries[1\u535c14]\uff0eLIU et al[14] recovered 50\uff05of water-soluble manganese from an electrolytic manganese residue fEMR)via a MFP using water\uff0eThis MFP\u2014based water washing technology could be industrially applied because it solves the problem of \u2018’water swelling\u201d\uff0ewhich commonly occurs in previous water washing technologies[1 4\uff0c1 5]\uff0eOn the basis of the previous work of LIU et al[1 4]\uff0cwe attempted to wash the EMR via a MFP using anolyte\uff0eIn 2009\uff0cthe MFP\u2014based technology on the leaching and recovery of manganese from EMR via a combination of anolyte washing with water washing was realized and resulted in a patent application being submitted(No\uff0eCN1 024700A) \u300e1 61\uff0eNote that several demonstrative operations have also been constructed in China based on this technology\uff0e However,the possibility of using this technology in the hydrometallurgical zinc process has never been investigated previously\uff0eIf this technology could be used in electrolytic zinc plants\uff0cthe thickening\uff0cpulping\uff0c second leaching\uff0cwashing\uff0cfiltering and pressing would be integrated and realized using a single MFR In addition\uff0cthe leaching of zinc from ZLR in the form of spent electrolyte washing would be performed under constant acid concentration via a continuous flow of spent electrolyte\uff0e Hence\uff0ethe feasibility of leaching and recovery of zinc from lcaching residue of zinc calcine based on MFP was investigated\uff0ccombining spent electrolyte washing with flesh water washing\uff0eFor this work\uff0ethe uniformity of filter cakes\uff0ewhich is directly related to the leaching result\uff0cwas examined\uff0eBased on this experimental result\uff0c the 1eaching and washing on extracting zinc from ZLR were subsequently studied\uff0e<\/p>\n
<\/p>\n
2 Experimental 623<\/p>\n
2\uff0e1 Materials The experimental study was performed using zinc calcine with a composition of 57\uff05zinc\uff0ewhich was purchased from Hunan Province\u3002 China\uff0e Spent electrolyte containing 1 60 g\uff0fL of H2S04 and 50 g\uff0fL of Zn\u201dwas used in all of the leaching experiments\uff0eUnder all examined conditions\uff0ethe zinc concentration was determined based on GB\uff0fT 14353\uff0e3-2010\u300e17]\uff0cand the hydrogen ion concen\u4ec3ation fH+\u3001was measured based on GB 6498\uff0e2-2001\u300e181\uff0eThe membrane filter press (KM470)was from Beijing ZSC Solid\u2014Liquid Separating Technology Co\uff0e\uff0cLtd\uff0e(China)\uff0cand the membrane plates (470 ml\uff0fl\u00d7470 mill)were from LENSER Filtration GmbH+Co\uff0e(Germany)\uff0e<\/p>\n
2\uff0e2 Experimental procedure The diagram of leaching and recovery of zinc from zinc calcine is presented in Fig\uff0e1\uff0e111e proper production process is described briefly as follows\uff0e1 1 leaching in stirred\uff0etank reactor\uff1aSpent electrolyte or sulfuric acid was added to the crashed zinc calcine to leach zinc ions from the ores and to obtain the ZnS04-contained slurry\uff0e2\u3001 filtration\uff1athe ZnS04-contained slurry was pumped into MFP through central feeding hole and filter pressed to obtain the filter cakes(i\uff0ee\uff0e\uff0cZLR)\uff1bnext\uff0cthe filtrate (1eaching liquor)entered the subsequent production process\uff0e3\u3001Re\uff0e1eaching in\u2163\u3010FP\uff1aSpent electrolyte at the desired temperature was pumped into the MFP and reacted with filter cakes to leach zinc again and simultaneously recover part of ZnS04\uff0e4)water washing\uff1a The filter cakes were washed again with flesh water to further recover ZnS04\uff0e5)pressing\uff1aWater with a pressureof 1 MPa was pumped into the membrane plates\uff0ewhich was maintained for 20 min to reduce the water content of filter cakes\uff0c and the pressed filter cakes were subsequently discharged from the MFP and transported to landfills\uff0eThe eluate obtained from spent electrolyte washing and flesh water washing steps were collected and returned to spent electrolyte tank and eluate collection tank\uff0crespectively\uff0e <\/span><\/p>\n 3 Results and discussion <\/span><\/p>\n 3\uff0e1 Filter cake formation To obtain a high zinc ex\u4ec3action rate and recovery rate using an MFP\uff0ethe most important step is to obtain uniform filter cakes\uff0eThe particle size of zinc calcine and sedimentation time\uff0ewhich are directly involved with the width of the filter chambers\uff0care the most important parameters regarding the uniformity of filter cake\uff0e Therefore\uff0cthe particle sizes of zinc calcine\uff0cas well as the width of the filter chamber were firstly selected\uff0eThe five\u2014spot test(upper left\uff0cbottom left\uff0ccenter,upper right\uff0c bottom right)was used for estimating the uniformity of the filter cakes by measuring the zinc content and thickness of the cakes at these selected points\uff0e Through observation of the filter cakes formed in the MFP,it is found that triangle cakes were easily formed using raw zinc calcine\uff0eThe particle size distribution of raw zinc calcines was measured and the corresponding result is presented in Table 1\uff0eThe presence zinc calcine of large particle size inhibits the formation of uniform cakes due to its good settleability\uff1a thus\uff0csmall size particles should be selected\uff0eChoosing the particle size of zinc calcine less than 106 gm\u4ec3\u3001able 1 1\u3002which could be obtained in actual production\uff0ca series of experiments regarding the filter cake formation were conducted\uff0eand the results are presented in Fig\uff0e2\uff0e From Fig\uff0e2\uff0cusing zinc calcines with particle sizes less than 1 06 gm\uff0cthe zinc content and filter cake thickness vary clearly at the five tested points when the filter chamber width is 40 mln\uff0csuggesting that the cake uniformity is poor under this condition\uff0cwhich might be due to long sedimentation time\uff0eWhen the filter chamber width is 30 lnnl\uff0ethe cake uniformity is improved significantly relative to the chamber width of 40 nun\uff0e When the filter chamber width is 20 mm\uff0cthe cake <\/span>uniformity is similar to the results obtained as the chamber width is 30 mm\uff0eThus\uff0eit can be clearly observed that the uniforlTl filter cakes could be formed by choosing the particle size of zinc calcine to be less than 1 06 Bm for filter chamber widths of 20 mm and 30 mill\uff0e As a result\uff0ethe zinc calcines with particle size 1ess than 1 06 Bm were used in the following experiments\uff0eThe processing capacity of MFP with 20 mm width chamber is 10wer than that with 30 toni width chamber\uff0eTherefore\uff0e combining the results of processing capacity and cake uniformity,the chamber width of 30 finn was selected in the following experiments\uff0e <\/span><\/p>\n 3\uff0e2 Leaching of zinc from zinc calcine In this lcaching process\uff0e1 00 L of spent electrolyte solution was added to a 300 L stainless steel drum equipped with a variable speed stirrer and then stirred for approximately 1 h at a speed of 60 r\uff0fmin\uff0eNext\uff0cthe 1eaching solution was adjusted by adding zinc calcine or sulfate acid until the final Zn\u201dconcentration of electrolyte was in the range of 130-140 g\uff0fL and the final H2S04 concentration was in the range of l\u4e002 g\uff0fL\uff0e Subsequently,the ZnS04-contained slurry was filtered using a MFE The analysis results of zinc calcine and ZLR are presented in 1\u2019ables 2 and 3\uff0erespectively\uff0e As presented in Table 2\uff0ethe grade of zinc calcine is 57\uff0e52\uff05\uff0ein which ZnO approximately accounts for 90\uff0e06\uff05of total zinc in mass\uff0eTable 3 indicates that in this process of leaching\uff0cmost of the Zn0 is converted to ZnS04\uff0cresulting in the dramatic decrease of the content of ZnO\uff0eAfter solid-liquid separation using the MFP\uff0e many insoluble materials are concentrated in the residue\uff0e The content of zinc in the leaching residue is higher than 20\uff05\uff0ccausing the extraction rate of zinc in this process to be less than 90\uff05\uff0eAnalysis of ZLR indicates that zinc iS mainly presented in the forills of ZnFe204\uff0cZnO and ZnS04\uff0cwhich in total account for uD to 80\uff05of the zinc<\/span>(Table 3)\uff0eThus\uff0ca secondary leaching process is required to recover the remaining zinc\uff0e<\/span><\/p>\n 3\uff0e3 Leaching of zinc from ZLR In this leaching process\uff0cthe zinc was extracted from ZLR obtained in Section 3\uff0e2 in the form of spent electrolyte washing using MFE To dissolve ZnFe204\uff0c strict leaching conditions\uff0csuch as high temperature (above 90\u3002C\u3001and high concentration of acid solution (100\u2014200 g\uff0fL)\uff0care required\uff0eUnder hi\u3002\u66f2temperature and high acid concentration conditions\uff0cthe extraction rate of zinc can increase to approximately 97\uff05[19\uff0c20]\uff0eTo enable a comparison with the extraction rate obtained in the traditional route\uff0ethe lcaching conditions in the present work are under a temperature in the range of 90 to 96 oC and an acid concentration in the range of 1 00 to 200 g\uff0fL\uff0eBecanse\u4e5fe leaching residues of zinc calcine were fixed in the chamber of the MFP\uff0ethe high reaction temperature condition was realized through heating of the spent electrolyte\uff0e Figure 3 shows the Zn\u201dand H2S04 concentrations with leaching time under atemperature in the range of 90 to 96 oC during the leaching process based on MFE From Fig\u30023\uff0ethe Zn\u201dconcentration is observed to obviously increase during the initial 5 min\uff0cfollowed by a decrease to 55\u7391after washing for 60 min and only a slight change around the level of 55 g\uff0fL in the following 30 min\uff0eConversely\u2019the H2S04 concentration obviously decreases during the initial 5 min\uff0efollowed by an increase to 11 7 g\uff0fL after washing for 60 min and then slight changes around the level of 120 g\uff0fL in next 30 min\uff0e Based on these above results\uff0cit can be concluded that the violently reaction of the leaching residue with the hot spent electrolyte only lasts for approximately 60 min\uff0e The analysis result of the residue after hot concentrated acid leaching for 90 min is presented in T2lble 4\uff0eClearlv\uff0e the zinc content in the residue reduces significantly from over 20\uff05(Table 3)to less than 1 0\uff05(Table 41\uff0eAs a consequence\uff0cthe zinc extraction rate 1ncreases to 97\uff05\uff0e \u7800Hs\uff0ethis result obviously demonstrates that using a MFP as a leaching reactor could not only ensure a high extraction rate but also reduce the leaching time compared with the traditional hot concentrated acid leaching\uff0eThe short leaching time using a MFP might be due to the constant reaction conditions of high temperature and high acid concentration during the whole process when using a MFE Based on the above results\uff0eadditional experiments on the leaching of zinc from ZLR were also conducted under low temperatures\uff0csuch as at 30 oC\uff0c60 to 70 oC\uff0c70 to 80 oC and 80 to 90 oC\uff0eto reduce the energy consumption further\uff0eThe corresponding results are presented in Fig\uff0e4\uff0e The zinc extraction rate at 30 oC is 92\uff0e67\uff05\uff0eand increases to 94\uff0e95\uff05at 60 to 70\u3002C\uff0eWhen the 1eaching temperature is further increased to 80 to 90\u3002C\uff0ethe ex\u4ec3action ratio increases to 95\uff0e56\uff05\uff0eThe temperature of spent electrolyte has an obvious effect on t11e zinc extraction ratio\uff0eHigh zinc extraction could be obtained by increasing the temperature of leaching\uff0cwhich is consistent wim the results of Ref\uff0ef191\uff0eUnder Iow temperatures\uff0cthe energy consumption is lower,the extraction ratio can not reach the traditional result of 97\uff05\uff0eIn conelusion\uff0ethe hot acid leaching only at 90 to 96 oC or above can achieve the ideal result(i\uff0ee\uff0e\uff0cmore than 97\uff05\u3001\uff0e <\/span><\/p>\n 3\uff0e4 Recovery of water-soluble zinc <\/span><\/p>\n The water-soluble zinc approximately accounts for 3\uff05of the total zinc in the residue after hot acid<\/span>leaching with MFP(Table 41\uff0eTo recover this part of the zinc\uff0ethe leaching residue was further washed with Water\uff0e Figure 5 shows that both the Zn2+and H\uff0cS04 concentrations of eluate decrease with increasing washing time\uff0eespecially in the initial 5 min\uff0eThese results indicate that Zn\u201dand H\uff0cS04 in the zinc residue could be quickly washed out by Water using the MFP\uff0e After washing for 25 min\uff0cthe final Znz+and H2S04 concentrations of eluate decrease to 0\uff0e05\u53fdand 1\uff0e25 g\uff0fL\uff0erespectively\uff0e The final residue obtained after being washed and <\/span>pressed merely contains 6\uff05of zinc\uff0ein which the water-soluble zinc only accounts for 0\uff0e07\uff05(Table 5)\uff0c suggesting that the majority of water-soluble zinc is recovered during the water washing process\uff0eCompared with the traditional hot concentrated acid leaching process\uff0cthe water-soluble zinc lost in the leaching residue iS very 10W\uff0e 3\uff0e5 Washing uniformity To estimate the washing results\uff0cthe washing uniformity of MFP was examined by measuring\uff0eboth the total zinc and the water-soluble zinc contents in the final residue\uff0eAs presented in Rlble 6\uff0eboth the total zinc and the water-soluble zinc contents change slightly at five selected points(upper left\uff0cbottom left\uff0ccenter,upper right\uff0cand bottom right)in the residue\uff0cindicating that the hot spent electrolyte and water washing are quite uniforiil\uff0eTherefore\uff0ethe zinc that can be extracted in zinc calcine and the Water-soluble zinc that can be recovered in the residue are completely extracted and recovered by USing the MFP\uff0e<\/span><\/p>\n 4 Conclusions<\/p>\n 1\u3011The use of a MFP is found to be completely feasible and effective to 1each and recover zinc from leaching residues ofzinc calcine\uff0e<\/p>\n 2\u3011The zinc calcines with particle size of less than 1 06 gm and MFP chambers with a width of 30 I\uff0fIlTI are proper for establishing unifornl filter cakes to obtain <\/span>acceptable leaching and recovery results\uff0e<\/span><\/p>\n 2 Experimental 623<\/p>\n 2\uff0e1 Materials The experimental study was performed using zinc calcine with a composition of 57\uff05zinc\uff0ewhich was purchased from Hunan Province\u3002 China\uff0e Spent electrolyte containing 1 60 g\uff0fL of H2S04 and 50 g\uff0fL of Zn\u201dwas used in all of the leaching experiments\uff0eUnder all examined conditions\uff0ethe zinc concentration was determined based on GB\uff0fT 14353\uff0e3-2010\u300e17]\uff0cand the hydrogen ion concen\u4ec3ation fH+\u3001was measured based on GB 6498\uff0e2-2001\u300e181\uff0eThe membrane filter press (KM470)was from Beijing ZSC Solid\u2014Liquid Separating Technology Co\uff0e\uff0cLtd\uff0e(China)\uff0cand the membrane plates (470 ml\uff0fl\u00d7470 mill)were from LENSER Filtration GmbH+Co\uff0e(Germany)\uff0e<\/p>\n 2\uff0e2 Experimental procedure The diagram of leaching and recovery of zinc from zinc calcine is presented in Fig\uff0e1\uff0e111e proper production process is described briefly as follows\uff0e1 1 leaching in stirred\uff0etank reactor\uff1aSpent electrolyte or sulfuric acid was added to the crashed zinc calcine to leach zinc ions from the ores and to obtain the ZnS04-contained slurry\uff0e2\u3001 filtration\uff1athe ZnS04-contained slurry was pumped into MFP through central feeding hole and filter pressed to obtain the filter cakes(i\uff0ee\uff0e\uff0cZLR)\uff1bnext\uff0cthe filtrate (1eaching liquor)entered the subsequent production process\uff0e3\u3001Re\uff0e1eaching in\u2163\u3010FP\uff1aSpent electrolyte at the desired temperature was pumped into the MFP and reacted with filter cakes to leach zinc again and simultaneously recover part of ZnS04\uff0e4)water washing\uff1a The filter cakes were washed again with flesh water to further recover ZnS04\uff0e5)pressing\uff1aWater with a pressureof 1 MPa was pumped into the membrane plates\uff0ewhich was maintained for 20 min to reduce the water content of filter cakes\uff0c and the pressed filter cakes were subsequently discharged from the MFP and transported to landfills\uff0eThe eluate obtained from spent electrolyte washing and flesh water washing steps were collected and returned to spent electrolyte tank and eluate collection tank\uff0crespectively\uff0e <\/span><\/p>\n 3 Results and discussion <\/span><\/p>\n 3\uff0e1 Filter cake formation To obtain a high zinc ex\u4ec3action rate and recovery rate using an MFP\uff0ethe most important step is to obtain uniform filter cakes\uff0eThe particle size of zinc calcine and sedimentation time\uff0ewhich are directly involved with the width of the filter chambers\uff0care the most important parameters regarding the uniformity of filter cake\uff0e Therefore\uff0cthe particle sizes of zinc calcine\uff0cas well as the width of the filter chamber were firstly selected\uff0eThe five\u2014spot test(upper left\uff0cbottom left\uff0ccenter,upper right\uff0c bottom right)was used for estimating the uniformity of the filter cakes by measuring the zinc content and thickness of the cakes at these selected points\uff0e Through observation of the filter cakes formed in the MFP,it is found that triangle cakes were easily formed using raw zinc calcine\uff0eThe particle size distribution of raw zinc calcines was measured and the corresponding result is presented in Table 1\uff0eThe presence zinc calcine of large particle size inhibits the formation of uniform cakes due to its good settleability\uff1a thus\uff0csmall size particles should be selected\uff0eChoosing the particle size of zinc calcine less than 106 gm\u4ec3\u3001able 1 1\u3002which could be obtained in actual production\uff0ca series of experiments regarding the filter cake formation were conducted\uff0eand the results are presented in Fig\uff0e2\uff0e From Fig\uff0e2\uff0cusing zinc calcines with particle sizes less than 1 06 gm\uff0cthe zinc content and filter cake thickness vary clearly at the five tested points when the filter chamber width is 40 mln\uff0csuggesting that the cake uniformity is poor under this condition\uff0cwhich might be due to long sedimentation time\uff0eWhen the filter chamber width is 30 lnnl\uff0ethe cake uniformity is improved significantly relative to the chamber width of 40 nun\uff0e When the filter chamber width is 20 mm\uff0cthe cake <\/span>uniformity is similar to the results obtained as the chamber width is 30 mm\uff0eThus\uff0eit can be clearly observed that the uniforlTl filter cakes could be formed by choosing the particle size of zinc calcine to be less than 1 06 Bm for filter chamber widths of 20 mm and 30 mill\uff0e As a result\uff0ethe zinc calcines with particle size 1ess than 1 06 Bm were used in the following experiments\uff0eThe processing capacity of MFP with 20 mm width chamber is 10wer than that with 30 toni width chamber\uff0eTherefore\uff0e combining the results of processing capacity and cake uniformity,the chamber width of 30 finn was selected in the following experiments\uff0e <\/span><\/p>\n 3\uff0e2 Leaching of zinc from zinc calcine In this lcaching process\uff0e1 00 L of spent electrolyte solution was added to a 300 L stainless steel drum equipped with a variable speed stirrer and then stirred for approximately 1 h at a speed of 60 r\uff0fmin\uff0eNext\uff0cthe 1eaching solution was adjusted by adding zinc calcine or sulfate acid until the final Zn\u201dconcentration of electrolyte was in the range of 130-140 g\uff0fL and the final H2S04 concentration was in the range of l\u4e002 g\uff0fL\uff0e Subsequently,the ZnS04-contained slurry was filtered using a MFE The analysis results of zinc calcine and ZLR are presented in 1\u2019ables 2 and 3\uff0erespectively\uff0e As presented in Table 2\uff0ethe grade of zinc calcine is 57\uff0e52\uff05\uff0ein which ZnO approximately accounts for 90\uff0e06\uff05of total zinc in mass\uff0eTable 3 indicates that in this process of leaching\uff0cmost of the Zn0 is converted to ZnS04\uff0cresulting in the dramatic decrease of the content of ZnO\uff0eAfter solid-liquid separation using the MFP\uff0e many insoluble materials are concentrated in the residue\uff0e The content of zinc in the leaching residue is higher than 20\uff05\uff0ccausing the extraction rate of zinc in this process to be less than 90\uff05\uff0eAnalysis of ZLR indicates that zinc iS mainly presented in the forills of ZnFe204\uff0cZnO and ZnS04\uff0cwhich in total account for uD to 80\uff05of the zinc<\/span>(Table 3)\uff0eThus\uff0ca secondary leaching process is required to recover the remaining zinc\uff0e<\/span><\/p>\n 3\uff0e3 Leaching of zinc from ZLR In this leaching process\uff0cthe zinc was extracted from ZLR obtained in Section 3\uff0e2 in the form of spent electrolyte washing using MFE To dissolve ZnFe204\uff0c strict leaching conditions\uff0csuch as high temperature (above 90\u3002C\u3001and high concentration of acid solution (100\u2014200 g\uff0fL)\uff0care required\uff0eUnder hi\u3002\u66f2temperature and high acid concentration conditions\uff0cthe extraction rate of zinc can increase to approximately 97\uff05[19\uff0c20]\uff0eTo enable a comparison with the extraction rate obtained in the traditional route\uff0ethe lcaching conditions in the present work are under a temperature in the range of 90 to 96 oC and an acid concentration in the range of 1 00 to 200 g\uff0fL\uff0eBecanse\u4e5fe leaching residues of zinc calcine were fixed in the chamber of the MFP\uff0ethe high reaction temperature condition was realized through heating of the spent electrolyte\uff0e Figure 3 shows the Zn\u201dand H2S04 concentrations with leaching time under atemperature in the range of 90 to 96 oC during the leaching process based on MFE From Fig\u30023\uff0ethe Zn\u201dconcentration is observed to obviously increase during the initial 5 min\uff0cfollowed by a decrease to 55\u7391after washing for 60 min and only a slight change around the level of 55 g\uff0fL in the following 30 min\uff0eConversely\u2019the H2S04 concentration obviously decreases during the initial 5 min\uff0efollowed by an increase to 11 7 g\uff0fL after washing for 60 min and then slight changes around the level of 120 g\uff0fL in next 30 min\uff0e Based on these above results\uff0cit can be concluded that the violently reaction of the leaching residue with the hot spent electrolyte only lasts for approximately 60 min\uff0e The analysis result of the residue after hot concentrated acid leaching for 90 min is presented in T2lble 4\uff0eClearlv\uff0e the zinc content in the residue reduces significantly from over 20\uff05(Table 3)to less than 1 0\uff05(Table 41\uff0eAs a consequence\uff0cthe zinc extraction rate 1ncreases to 97\uff05\uff0e \u7800Hs\uff0ethis result obviously demonstrates that using a MFP as a leaching reactor could not only ensure a high extraction rate but also reduce the leaching time compared with the traditional hot concentrated acid leaching\uff0eThe short leaching time using a MFP might be due to the constant reaction conditions of high temperature and high acid concentration during the whole process when using a MFE Based on the above results\uff0eadditional experiments on the leaching of zinc from ZLR were also conducted under low temperatures\uff0csuch as at 30 oC\uff0c60 to 70 oC\uff0c70 to 80 oC and 80 to 90 oC\uff0eto reduce the energy consumption further\uff0eThe corresponding results are presented in Fig\uff0e4\uff0e The zinc extraction rate at 30 oC is 92\uff0e67\uff05\uff0eand increases to 94\uff0e95\uff05at 60 to 70\u3002C\uff0eWhen the 1eaching temperature is further increased to 80 to 90\u3002C\uff0ethe ex\u4ec3action ratio increases to 95\uff0e56\uff05\uff0eThe temperature of spent electrolyte has an obvious effect on t11e zinc extraction ratio\uff0eHigh zinc extraction could be obtained by increasing the temperature of leaching\uff0cwhich is consistent wim the results of Ref\uff0ef191\uff0eUnder Iow temperatures\uff0cthe energy consumption is lower,the extraction ratio can not reach the traditional result of 97\uff05\uff0eIn conelusion\uff0ethe hot acid leaching only at 90 to 96 oC or above can achieve the ideal result(i\uff0ee\uff0e\uff0cmore than 97\uff05\u3001\uff0e <\/span><\/p>\n 3\uff0e4 Recovery of water-soluble zinc <\/span><\/p>\n The water-soluble zinc approximately accounts for 3\uff05of the total zinc in the residue after hot acid<\/span>leaching with MFP(Table 41\uff0eTo recover this part of the zinc\uff0ethe leaching residue was further washed with Water\uff0e Figure 5 shows that both the Zn2+and H\uff0cS04 concentrations of eluate decrease with increasing washing time\uff0eespecially in the initial 5 min\uff0eThese results indicate that Zn\u201dand H\uff0cS04 in the zinc residue could be quickly washed out by Water using the MFP\uff0e After washing for 25 min\uff0cthe final Znz+and H2S04 concentrations of eluate decrease to 0\uff0e05\u53fdand 1\uff0e25 g\uff0fL\uff0erespectively\uff0e The final residue obtained after being washed and <\/span>pressed merely contains 6\uff05of zinc\uff0ein which the water-soluble zinc only accounts for 0\uff0e07\uff05(Table 5)\uff0c suggesting that the majority of water-soluble zinc is recovered during the water washing process\uff0eCompared with the traditional hot concentrated acid leaching process\uff0cthe water-soluble zinc lost in the leaching residue iS very 10W\uff0e 3\uff0e5 Washing uniformity To estimate the washing results\uff0cthe washing uniformity of MFP was examined by measuring\uff0eboth the total zinc and the water-soluble zinc contents in the final residue\uff0eAs presented in Rlble 6\uff0eboth the total zinc and the water-soluble zinc contents change slightly at five selected points(upper left\uff0cbottom left\uff0ccenter,upper right\uff0cand bottom right)in the residue\uff0cindicating that the hot spent electrolyte and water washing are quite uniforiil\uff0eTherefore\uff0ethe zinc that can be extracted in zinc calcine and the Water-soluble zinc that can be recovered in the residue are completely extracted and recovered by USing the MFP\uff0e<\/span><\/p>\n 4 Conclusions<\/p>\n 1\u3011The use of a MFP is found to be completely feasible and effective to 1each and recover zinc from leaching residues ofzinc calcine\uff0e<\/p>\n 2\u3011The zinc calcines with particle size of less than 1 06 gm and MFP chambers with a width of 30 I\uff0fIlTI are proper for establishing unifornl filter cakes to obtain <\/span>acceptable leaching and recovery results\uff0e<\/span><\/p>\n \n","protected":false},"excerpt":{"rendered":" 1 Introduction Zinc sulfide ores are the main source of 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<\/p>\n