Study on Removal of Water-soluble Chloride from Crude Zinc Oxide and the Dechlorination of Wastewater by Synthesis of LDHs

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1 V-01-3 Study on Removal of Water-soluble Chloride from Crude Zinc Oxide and the Dechlorination of Wastewater by Synthesis of LDHs Wai-Hao Lee 1 Ta-Wui Cheng 2 Teng-Ker Hsu 3 Chia-Cheng Wu 4 1. Doctoral Student, Graduate Institution of Technology Engineering, National Taipei University of Technology. 2. Professor, Institute of Mineral Resources Engineering, National Taipei University of Technology. 3. Manager, CHC Resource Corporation 4. Profession Engineer, CHC Resource Corporation * Corresponding author: Wai-Hao Lee Graduate Institution of Technology Engineering, National Taipei University of Technology, Taiwan ext2708 glowing955146@hotmail.com(wai-hao Lee). Abstract:The fine metal and chlorides containing flue dust from electric arc furnace (EAF-D) using recycled scrap is a major environmental problem in steel industry. Most of the EAF-D is treated by pyrometallurgical process such as Waelz-Process. As product crude zinc oxide (C-ZnO) is generated with high content on chloride. In this study the experiments of removing soluble chlorides from crude zinc oxide by wet scrubbing wrer carried out in a pilot plant. The dechlorination of wastewater by adding calcium hydroxide and sodium aluminate to form LDHs (Layer Double Hydroxides) was also investigated. The results show that more than 80% of chloride in crude zinc oxide can be removed by wet scrubbing. The rest chloride content is less than 1%. Moreover, over 99% of chloride can be removed after 3-stage treatment. At the mean time, the heavy metal removal is also significant. Keyword: EAF dust Crude Zinc Oxide Water washing LDHs. Introduction In Taiwan, there s about 160 thousand tons of electric arc furnace dusts(eaf-d) every year. Crude zinc oxide is generated as the product from the pyrometallurgical treatment of the EAF-D. Classic chemical composition of EAF-D is shown in table. 1 which indicates that zinc and iron are the major components of EAF-D. The zinc content exists in EAF-D in form of zinc oxide and zinc ferrite (ZnFe 2 O 4 ). Hence, EAF-D is one of the main sources of zinc oxide. [1] Table 1. Chemical composition of classic EAF dusts Element Weight percentage(wt%) Element Weight percentage(wt%) Fe 18~27 Mn 1.3~2.8 Cu 0.2~0.3 P 0.08~0.20 Zn 20~33 Na 1.5~1.8 Pb 2.5~4.0 Ni 0.02~0.07 Ca 3.7~5.5 K 1.0~1.7 Si 4.8 Cd Mg 1.0~1.2 Cl 3.3 Al 0.4~0.5 Cr 0.2~0.3 Due to the chloride content in raw scrap and additive in EAF steel making process, EAF-D contains zinc as crude zinc oxide after cooling. This leads to high chloride content in C-ZnO up to 15% which causes also up to 3% of chloride. [2] In a pyrometallurgical difficulties for the further reuse such as thermal process, the volatile chloride is collected together with corrosion, accumulation in process and Dioxin emission. 562

2 The removal of chloride from C-ZnO has become an important issue. Table. 2 Classic Chemical composition of C-ZnO Element Zn Fe Pb Cl Weight percentage(wt%) 40-60% 15-25% 5-10% 5-15% NaCl Crystal phase ZnO, ZnFe 2 O 4, ZnCl 2 ZnFe 2 O 4 PbO, PbCl 2 KCl LDHs are mainly formed by divalent and trivalent metal cations and other anions. Due to their special layer structure and ionic composition, LDHs exhibit ion exchange ability and are often used in wastewater treatment. LDHs structure is shown in Fig.1. Fig. 1 LDHs schematic structure [3] During the formation, the anion exchange ability of LDHs can bind the other cations anions in water. This could provide an alternative method to remove various comtaminations from wastewater and to produce a reusable solid residue at the same time. content were also used for the pilot test. The chemical compositions are shown in Tab.X. Table 2. Crude zinc oxide main chemical composition in removal of water-soluble chloride experiment. Element Weight percentage(wt%) Material and Experiments The C-ZnO samples used in this study were collected in a EAF-D treatment facility in Taiwan. The main chemical composition of C-ZnO is listed in Tab.X. Besides, three C-ZnO samples with different zinc Zn 42.1 Fe 11.1 Pb 3.2 Cl 8.8 Table 4. Crude zinc oxide main chemical composition in pilot-scale experiment. No. 50 % Zn-crude zinc oxide 42 % Zn-crude zinc oxide 33 % Zn-crude zinc oxide Element Weight percentage(wt%) Weight percentage(wt%) Weight percentage(wt%) Zn Fe Pb Cl Experimental works were divided into two groups: Removal of soluble chlorides from C-ZnO by wet scrubbing Wastewater dechlorination by synthesis of LDHs 563

3 I. Removal of water-soluble chloride from C-ZnO This stage experiment was using scrubbing to removal water soluble chloride from crude zinc oxide. This experiment did not add any chemical agent, that the waste water processing cost could be cutting down. When high concentration slurry with vigorous scrubbed in agitator, that could let particle bearing strongly shearing force, and making the impurities that adhered on the particles surface (including heavy metal, water-soluble / insoluble chloride etc.) shedding because particle impact each other. The crude zinc oxide chemical composition using in this stage was shown in table 2, experimental procedure was shown in Fig. 1 and experimental parameters as shown table 3. This stage experiment was finding out the optimal scrubbing concentration (liquid - solid ratio ) and scrubbing time. The C-ZnO was processed by wet scrubbing without adding chmical reagent. The concept of scrubbing is the based on the assumption that the collision probability of particles increases with increasing solid content in slurry. By grinding with each other, the impurities on the particle surface can be removed largely and the chloride removal can thus also improved. The parameters of solid-liquid-ratio (L/S) and scrubbing time were investigated. The C-ZnO sample were firstly dried at 100 C for 24hr. The chloride content of samples was determined according to the standard method CNS Fig.2 and shows the experimental procedures of wet scrubbing test in lab scale and the teat parameters of L/S ratio and scrubbing time are listed in Tab.2. Table 3. Removal of water-soluble chloride from crude zinc oxide experimental parameters Removal of water-soluble chloride experimental parameters C:slurry concentration T:stirring time Experiment No. Slurry concentration (Liquid-Solid ratio) Stirring ZnO-C1T1 1 1 min ZnO-C1T3 1 3 min ZnO-C1T5 1 5 min ZnO-C1T7 1 7 min ZnO-C1.5T min ZnO-C2T3 2 3 min ZnO-C2.5T min Fig. 2 Removal of water-soluble chloride from crude zinc oxide experiment procedure 564

4 After determining the optimal scrubbing parameters in labboratory scale, these were transferred into a test in pilot plant. There C-ZnO samples with different zinc content (33%, 40%, 50%) were test respectively. Fig.3 shows the flow chart of procedure. Fig. 3 Crude zinc oxide pre-treatment pilot-scale experiment procedure After drying at 100 C for 24hr, the chloride contents of the products were than determined. wastewater chemical composition was shown in table 5. The wastewater generated in the formal tests were used II. Wastewater dechlorination through synthesis LDHs for these experiments. Multi-stage treatment through synthesis LDHs for removing chloride from wastewater was tested respectively. The experimental procedure is This stage experiment was using the wastewater from shown in Fig.4. The chemical composition of [Removal of water-soluble chloride from crude zinc oxide] experiment to dechlorination. In this experiment would using multi-stage dosing, through synthesis wastewater is listed in Tab.5 (analyzed according to standard method NIEA W407.51C). The test parameters are shown in Tab.6. LDHs to dechlorination from wastewater. The Table 5. Wastewater chemical composition Element Cl Ca Al Heavy metal Zn Pb Cr Cd Concentration Unit : (mg/l) 565

5 Fig. 4 Wastewater dechlorination by synthesis LDHs experiment process Table 6. Wastewater dechlorination by synthesis LDHs experiment parameters 1st stage Dosing (1st) Item Reaction ph Reaction time Reaction Zn/Al Stirring speed (hr) temperature mole ratio (rpm) ( ) Condition nd stage Dosing (2nd) Item Reaction ph Ca/Cl mole ratio Al / Cl mole ratio Stirring speed (rpm) Reaction temperature ( ) Reaction time (hr) Condition rd stage Dosing (3rd) Item Reaction ph Ca/Cl mole ratio Al/Cl mole ratio Stirring speed (rpm) Reaction temperature ( ) Reaction time (hr) Condition Results and Discussion I. Removal of water-soluble chloride from crude zinc oxide This stage experiment divided into two part to discussion, which were the effect on chloride 566

6 removal efficiency in different scrubbing time efficiency would not increase when adding scrubbing and scrubbing time. time. Because, when scrubbing time over 3 min, particles Scrubbing time parameters effect on the chloride had enough time to hit each other, but did not have removal efficiency enough water to dissolve the chloride, so that, the Effect of scrubbing time on chloride removal chloride removal efficiency could not increase. Chloride removal efficiency was shown in table 7 and fig. Chloride removal in dependence on scrubbing time is 5. As the result shown, when scrubbing time in 1 min shown in Tab.7 and Fig.5. It is obvious that the chloride had the worst chloride removal efficiency than other removal reached a maximal value after 3 min of scrubbing time. Because, when scrubbing time in 1 min, scrubbing. After 1 min of scrubbing, the retention time is particles did not have enough time to hit each other, that not enough for the dissolution of chloride. If the particle surface still residual some chloride. When scrubbing time is extended to 5 and 7 min, the chloride scrubbing time over 3 min that chloride removal removal didn t increase due to the lack of water. efficiency could reach 76 %, and the chloride removal Table 7. Scrubbing time parameters effect on the chloride removal efficiency Chloride content ( wt.% ) Chloride removal efficiency(%) Untreatment Crude zinc oxide ZnO-CT-1 (1 min) ZnO-CT-2 (3 min) ZnO-CT-3 (5 min) ZnO-CT-4 (7 min) Cl Removal efficiency ( % ) Cl Removal efficiency( % ) Cl content in crde zinc oxide ( % ) Raw 1 min 3 min 5 min 7 min Stirring time Cl content in crde zinc oxide ( % ) Fig. 5 Scrubbing time parameters effect on the chloride removal efficiency Scrubbing concentration parameters effect on the chloride removal efficiency Effect of L/S ratio on chloride removal Chloride removal efficiency was shown in table 8 and fig. 6. As the result shown, when scrubbing L/S ratio in 1.5 the chloride removal efficiency was higher than other scrubbing L/S ratio, and the chloride removal efficiency was 80%. Because, when scrubbing L/S ratio less than 1.5, the slurry concentration was too high, even though particles hit each other, the chloride release form particle surface, but did not have enough water to dissolve it. When scrubbing L/S ratio over than 1.5, the slurry concentration was too thin, particles could not have enough chance to hit each other, so that particle surface still residual some chloride. Chloride removal in dependence on L/S ratio is shown in Tab.8 and Fig.6. The chloride removal, as shown, increases firstly when the L/S ratio rises from 1 to 1.5 due to the good solubility of chloride salt in water. The removal efficiency reaches as high as 80%. The removal of chloride, on the other hand, decreases with the increasing L/S ratio from 1.5 to 2.5. The reason for it is the weak collision between particles due to the low solid concentration. 567

7 Table 8. Scrubbing L/S ratio parameters effect on the chloride removal efficiency Chloride content ( wt.% ) Chloride removal efficiency(%) Untreatment Crude zinc oxide Z n O - C T - 2 ( L / S = 1 ) Z n O - C T - 5 ( L / S = 1. 5 ) Z n O - C T - 6 ( L / S = 2 ) Z n O - C T - 7 ( L / S = 2. 5 ) Cl Removal efficiency ( % ) Cl Removal efficiency( % ) Cl content in crde zinc oxide ( % ) Raw 1:1 1.5:1 2:1 2.5:1 Slurry concentration( Liquid-Solid ) Cl content in crde zinc oxide ( % ) Fig. 6 Scrubbing L/S ratio parameters effect on the chloride removal efficiency Tests in a pilot plant Chloride removal efficiency of this test series was shown in table 9. As the result shows, the chloride removal efficiency could reach 85% in different grade of crude zinc oxide. As the chloride content increase, the chloride removal efficiency increase as well. Table 9. Chloride removal efficiency on using optimal scrubbing parameters in pilot-scale experime nt Chloride content ( wt.% ) -Origin Chloride content ( wt.% )- after process Chloride removal efficiency(%) 50 % Zn-crude zinc oxide % 42 % Zn-crude zinc oxide % 33 % Zn-crude zinc oxide % II. Wastewater dechlorination treatment through synthesis LDHs The experiments were carried out by adding sodium aluminate and calcium hydroxide in different stages (multi-stage). Fig.7 shows the removal of chloride from scrubbing wastewater in different stage of treatment. As shown, the 2 nd stage by adding calcium hydroxide exhibts the best efficiency. Over 60% of chloride can be bound in LDHs and removed from wastewater. After 3 rd stage and treatment, more than 90% of chloride were removed. Due to the ion exchanging ability of LDHs, the heavy metals in wastewater are also removed at the same time. The removal of Zn, Cd, Cr and Pb are shown in Tab

8 Fig. 7 Wastewater dechlorination efficiency in different stage. After dosing residual in water Table 10. Cl and heavymetal content in different dosing stage Cl and heavymetal content Elements content ( ppm ) Item Zn Cl Cd Pb Cr Original wastewater RW-3-1st RW-3-2nd RW-3-3th XRD patterns of the sludge from different stage are shown in Fig.8. As the result shown, the main mineral phase of sludge are different phases of Friedel s salts ( Ca 4 Al 2 O 6 Cl 2 10H 2 O ) Portlandite ( Ca(OH) 2 ) and Katoite ( Ca 3 Al 2 (OH) 12 ). According to the results, the Friedel s salt crystal 1st-stage and 3rd-stage, because in 2nd-stage the calcium hydroxide dosed weight was higher than 1st-stage and 3rd-stage, Cl and Ca ion could easily synthesis Friedel s salt, this result also could explain why in the 2nd-stage have the highest dechlorination efficiency. phase intensity in 2nd-stage sludge was higher than 569

9 Fig. 8 XRD patterns of the sludge from different stage ( a ) 1st-stage ( b ) 2nd-stage ( c ) 3rd-stage. Conclusions Removal of water-soluble chloride from crude zinc oxide 1. The optimal scrubbing parameter is scrubbing for 3 min with L/S ratio of 1.5. The chloride removal efficiency could reach 80%. 2. According to the pilot-scale test, the Chloride removal efficiency could reach over 85% when using the optimal scrubbing parameter on different grade of crude zinc oxide. Wastewater dechlorination through synthesis LDHs 1. Using multi-stage treatment of wastewater, dechlorination efficiency could reach 91%, Zn ion removal efficiency could reach 98%, Cd ion removal efficiency could 100%. 2. According to XRD analysis results, the sludge crystal phase was CaAlCl-LDHs. 3. Using synthesis LDHs to dechlorination in wastewater, could removal heavy metals at the same time. References 1. C.L. Hung et al, Zinc smelting and recycling, Mining & Metallurgy, vol.53, pp.27-37, Y.T Lin et al, The removement of chlorine in crude zinc oxide by pumping and counter current system, Resources and Environment Symposium, pp , C.Y. Wu, A study on Hydrotalcite zinc aluminum laminates growth and supramolecular Theoretical, Master Thesis, Beijing University of Chemical Technology, Beijing,

10 V-02-4 The Research on Primary Sedimentation Sludge Reduction with the Addition of Liquid Fertilizer Chi-Kang Lin, Chia-Ji Teng, Chiu-Yi Chan, Yen-Hsiang Peng, Chi Hsiao, Yu-Syuan Sie Department of Environmental Engineering, Tungnan University, No152, Sec.3th, Pei-Shen Rd., Shen-Kun Village, New Taipei City, Taiwan ABSTRACTS: This study examines the efficiency and mechanism of reduction of primary sludge in the primary sedimentation tank with the addition of liquid fertilizer, molasses and acid-base reaction agent. The liquid fertilizer addition ratio varies from 60%, 50% and 40%. Each of the three ratio samples was tested in both 2.0 and 4.0 hours of continuous flow reaction of influent times. The study also measured the change in ph, ORP, TS, VFA and odour in basin before and after the continuous flow reaction in order to analyze the effect of sludge reduction. The result found that the volume of primary sludge decreased significantly with the addition of liquid fertilizer while the most optimal outcome resulted in having the liquid fertilizer addition ratio at 60% and the influent time period of addition of liquid fertilizer in continuous mode at 4 hours. In conclusion, the study found that liquid fertilizer, acid-base reaction agent and VFA have significant effects on the reduction of sludge in primary sedimentation tank. The major component of VFA produced from this experiment was acetic acid. Keywords Primary Sedimentation Sludge, Liquid Fertilizer, Volatile Fatty Acid (VFA), Oxidation Reduction Potential (ORP) 1. INTRODUCTION The treatment for solid wastes including the primary sedimentation sludge (P. S. S.) from sewage treatment plant has been getting more serious with the higher growth of population and industries recently. Taiwan EPA (2011) indicated that the insufficient treatment facility for nightsoil treatment plants was a major concern in Taiwan. A total 327,328 tons of nightsoi were produced every year in Taiwan. There was only 92,115 tons transported to nightsoil treatment plants, and 219,473 tons of that conveyed to sewage treatment plant, the other was served as the sources of liquid fertilizer (L. F.), seepage from composting processes of food wastes was comprised of rich grease and salinity, as well as organic compounds such as carbohydrates, carboxylic acid and protein. High strength and improperly disposal of L. F. which was hardly to be turned into fertilizer led to high risk of contamination to receiving water and soils. It was discovered that reduction of P. S. S. in the primary sedimentation tank could be done by addition of L.F., as claimed by EPB of New Taipei City This study examines the efficiency and mechanism of reduction of primary sludge (P. S.) in the primary sedimentation tank with the addition of L.F generated from garbage fermentation. 2. MATERIALS AND METHODS Each of the three ratio samples was tested in both 2.0 and 4.0 hours of continuous flow mode to examine optimum operating times and the P. P. S. reduction effects. (2). L. F. and molasses addition ratio In this stage L. F. and molasses were mixed by ratio (L.F to molasses) of 1:1, 3:1 and 5:1 as well as the mixed liquid and P. P. S. with the ratio of 60:40% and 40:60% (V/V), to investigate the effects of molasses on reduction of L.F. (3). Acid-base reagents test In this experiment some acid-base reaction reagents were added. This L. F., Sulfuric acid, Nitric acid, Sodium hydroxide and Drano max gel (ph=13) mixed with L.F. and P. P. S (60%:40% and 40%:60%, V/V). Each of the samples was tested in 4.0 hours of continuous flow mode to examines effects and mechanism of reduction of P. P. S Procedures There were several stages shown as following (1). Fundamental characteristics analysis of L.F. and P.S.S. (2). Addition ratios of L.F., molasses and basic and acidic reagents. (3). Experiment results comparison to investigate the factors affecting sludge reduction. (4). Sludge reduction mechanisms analysis as well as L.F. subsequent passage. 2.1 Research content (1). L. F. addition ratio The same initial amount of sludge, L.F was added at the volume of 40% (V/V) of reaction tank (V / V) the L. F. and P. S. S as well as the same volume of sludge. The L. F. to P.S.S ratio varies from 6 to 4, 4to 6, and 5 to