The Influence Factors and Responding Countermeasures on the Nitration of Copper Extractants

The Influence Factors and Responding Countermeasures on the Nitration of Copper Extractants
XU Zhi-gang, ZOU Qian, LI Jian, WANG Chao-hua (Hallochem Group, Solvent Extraction Engineering Research Center, Chong Qing 401221, China)
Abstract The nitration and degradation of copper extractants in the nitrate extraction system were studied. The effect of nitrate concentration, pH of the feed solution, temperature of the extraction system and modifiers on the nitration of the copper extractants were investigated. Two types of anti- nitration reagents were developed and their anti-nitration ability in the nitrate system was investigated. Results showed that the anti-nitration reagents can significantly enhance the anti-nitration ability for Copper extractants. In this work, the measures and methods for decreasing the nitration were suggested, which showed a good way for the hydrometallurgy plants to select the right copper extractants and reduce the nitration of the extractants. Key words: Copper extractants; Nitration; Influence factors; Anti-nitration reagents; Countermeasures
There are a variety of copper ore leaching methods, such asacid leaching[1-6], alkali leaching[7-9], seawater leaching[10-11], pressure leaching[12],oxidative leaching[6,9], bioleaching[13-14], etc. One of the mostcommon is the acid leaching.In acid leaching, sulfuric acid is used most frequently. But without pretreatment, it is difficult to leach sulfide ore with sulfuric acid, while nitrate leaching can often get a better leaching rate[15-16], therefore, the application of nitrate leachingis expanded constantly. Generally, nitrate leaching solution contains a certain amount of nitrate, some ore itself also contains nitrate, so even leaching with sulfuric acid, the leaching solution still contains nitrate .Under acidic conditions, nitrate will react with hydroxyoxime extractant, after nitration, strip ability of extractant is weaken, which greatly reduces the net copper transfer. The nitration can also lead to a slow extraction kinetics, worse phase separation and Cu2+/Fe2+ selective [17]. The stability of extractant after nitration is very poor, and the degradation of extractant is very fast under acidic (particularly high acidic) conditions[18]. How to prevent or reduce the damage of nitrate and improve the extractant efficiency attracts much attention from hydrometallurgy plants. The purpose of this study was to investigate the influence factors of copper extractants nitration, the anti-nitration reagents, and the measures for preventing and decreasing the nitration. 1 Experiment
1.1 Reagent 2-hydroxy-5-nonyl-benzaldoxime(aldoxime), 2-hydroxy-5-nonylacetophenone oxime (ketoxime), solvent extraction diluents Mextral DT-100 provided by Hallochem Group. 2,2,4-Trimethylpentanediol diisobutyrate (TXIB)—bought from Eastman. Tridecyl alcohol (TDA)-- bought from Shanghai Jinjinle Industry Co.,Ltd. 1.2 Apparatus

Synchronous magnetic stirrer(Shanghai Sile instrument Co.,Ltd.), full automatic digital constant temperature shaking table(Shanghai Huyueming Scientific Instruments Co.,Ltd), Agilent 1200 HPLC, UV , AAS 1.3 Method 1.3.1 Experimental method Under a certain temperature, the organic (10% v/v) and equal volume of simulated leaching solution (containing Cu2+ 35 g/L) with different nitrate concentration and acidity were continuously mixed. The extractant’s maximum copper loading was measured as MAXori before running. The maximum copper loading of organic was monitored periodically. Sulfuric acid (200 g/L, stripped 3 times) and hydrochloric acid (4N) were used to strip respectively, and the corresponding concentration of copper was recorded as MAX200, MAXHCl. After nitration, extractant can only be stripped with HCl(4N). 1.3.2 Analytical method A. Determination of copper concentration Macro copper content can be measured by titration method(EDTA),trace copper content can be measured by spectrophotometric method B. Calculation of nitration amount The percentage of nitration (%)=（MAXori- MAX200)/ MAXori*100% The natural degradation of the extractant under acidic conditions is ignored in the above equation since it is slow below 40 ℃. 2. Results and discussion 2.1The influence factors on the nitration of hydroxyoxime extractants 2.1.1 Extractants composition Under the same conditions, for the nitration speed: aldoxime, TXIB or TDA modified aldoxime were relatively fast; NP modified aldoxime, compound of aldoxime and ketoxime were relatively slow; ketoxime was slowest.
Fig.1 Nitration percentage of different extractant at different running time Experiment condition： H2SO4：180g/L，NO3-：20g/L，T=30℃。

As shown in Fig.1, after running for 35hours,for the percentage of nitration: aldoxime, TXIB modified aldoxime were nearly 100%, TDA modified aldoxime was over 80%, mixture of aldoxime and ketoxime was about 40%, ketoxime was less than 25%. 2.1.2 Nitrate concentration The nitration speed of extractant was closely related to the nitrate concentration. In strong acid （180g/L） and weak acid （pH=2.0） conditions， the nitration of aldoxime， TDA or TXIB modified aldoxime at different nitrate concentration of 10,20,30 and 40g/L were investigated. The results were shown in Table1 and Table2. Table1 Complete nitration time of extractants in strong acid（T=30℃） H2SO4 NO3TDA TXIB Aldoxime Concentration Concentration + Aldoxime + Aldoxime 180g/L 10g/L 55h 49h 48h 180g/L 20g/L 31h 27h 26h 180g/L 30g/L 15h 8h 7h 180g/L 40g/L 9h 6h 5h Table 2 The extractants nitration percentage after running for 50 days in weak acid TDA TXIB Aldoxime Condition NO3Concentration + Aldoxime + Aldoxime 10g/L 0.3% 0.4% 0.6% pH=2.0 20g/L 0.8% 0.9% 1.0% 30g/L 1.9% 2.1% 2.5% T=30℃ 40g/L 2.4% 3.8% 4.3% As shown in Table 1, in strong acid （180g/L）condition, with the increase of the nitrate concentration, extractant complete nitration time is getting shorter, that means the nitration speed of extractant is getting faster. As shown in Table 2, in weak acid（pH=2.0）condition, the nitration speed of extractant is also getting faster with the increase of the nitrate concentration.
2.1.3 Feed acidity The influence of feed acidity on nitration speed of extractant is significant. The higher the acidity, the faster the nitration speed, conversely, the slower the nitration speed. Table 3 The extractants nitration percentage after running for 50 days(T=40℃) NO3Feed TDA TXIB Aldoxime Concentration Acidity + Aldoxime + Aldoxime 30g/L pH=2.3 0.84% 0.96% 1.08% 30g/L PH=1.9 3.98% 4.13% 4.81% 30g/L pH=1.5 5.92% 6.63% 7.12%

Fig.2 Nitration percentage of extractant at different running time in weak acid condition Experiment condition：H2SO4：10g/L，NO3-：30g/L，T=40℃。
Fig.3 Nitration percentage of extractant at different running time in strong acid condition Experiment condition： H2SO4：180g/L，NO3-：30g/L，T=40℃。 When the nitrate concentration is 30g/L, pH=1.5～2.3, the nitration speeds of aldoxime, TXIB or TDA modified aldoxime were relatively slow. When pH=2.3, after running for 50days, the nitration percentage was low for each extractant, the highest was only about 1%. When pH=1.5, the nitration speed accelerated slightly, the highest percentage of nitration was 7.12%.But when the acidity was 10g/L, the nitration speed accelerated significantly, after running for 648hours,for the percentage of nitration: aldoxime and modified aldoxime were 100%, mixture of aldoxime and ketoxime was over 60%. When the concentration of sulfuric acid was 180g/L, nitrification speed increased sharply, after running for 7hours, for the percentage of nitration: aldoxime, TXIB modified aldoxime were over 90%, TDA modified aldoxime was over 75%, even the relatively stable mixture of aldoxime and ketoxime was nearly 30%. The above results show that the higher the acidity, the faster the nitration rate. 2.1.4 Running temperature The reaction between HNO3 and H2SO4 can be described by the following equation: HNO3 +H2SO4→ NO2+ +H2O + HSO4-

This reaction can generate NO2+, and the nitrification reaction mechanism is electrophilic substitution reaction between NO2+ and hydrogen on benzene ring. With the increase of temperature, there are more chances for NO2+ to contact with benzene ring, which accelerates the nitration speed.
Fig.4 Comparison of nitration speed of extractants at different temperature Experiment condition:NO3-：20g/L，H2SO4:180g/L，T=25℃，30℃, 35℃ The above results showed that, with the increase of temperature, nitration speed of different extractants all increased obviously. 2.2 Anti- nitration reagents AN1 and AN2 2.2.1 The influence of AN1 and AN2 on the anti-nitration ability of extractants When the concentration of H2SO4 is 180g/L , concentration of HNO3 is 10g/L,20g/L,30g/L or 40g/L, temperature is 30℃, the influence of AN1 and AN2 on the anti-nitration ability of aldoxime ， TDA or TXIB modified aldoxime and mixture of aldoxime and ketoxime were investigated. Results were shown in Fig.5 to Fig.8.
Fig.5 The influence of anti- nitration reagents on the anti-nitration ability of aldoxime Experiment condition: H2SO4：180g/L，NO3-：30g/L，T=30℃

Fig.6 The influence of anti- nitration reagents on the anti-nitration ability of TXIB modified aldoxime Experiment condition:H2SO4:180g/L,NO3-:10,20,30 and 40g/L, T=30℃
Fig.7 The influence of anti-nitration reagents on the anti-nitration ability of TDA modified aldoxime Experiment condition：H2SO4: 180g/L，NO3-: 30 g/L, 40g/L, T=30℃

Fig.8 The influence of anti- nitration reagents on the anti-nitration ability of mixture of aldoxime and ketoxime Experiment condition：H2SO4: 180g/L, NO3-: 10g/L, 20g/L, T=30℃ The above results show that, AN1 and AN2 has significantly anti-nitration ability to aldoxime extractants such as aldoxime, TXIB or TDA modified aldoxime, and AN2 has stronger anti-nitration ability than AN1. The Fig.6 results show that, when the concentration of H2SO4 is 180g/L, the lower the nitrate concentration, the stronger for AN1 and AN2 to enhance the anti-nitration ability of extractants. The Fig.6 and Fig.8 results show that, when the nitrate concentration is 10g/L or 20g/L,the anti-nitration reagents can reduce the nitration speed by one time or even more, that means the addition of AN1 and AN2 can significantly enhance the anti-nitration ability of extractants. 2.2.2 The influence of anti-nitration reagents on the performance of extractants 2.2.2.1The influence of anti-nitration reagents on the phase separation performance of extractants The addition of anti-nitration reagent should not change the physical properties of the extractant, especially should not have obvious negative effect, otherwise it is meaningless. Phase separation is one of the most important physical properties of extractant. When other conditions remained unchanged, the influence of AN1 or AN2 on the extraction or strip phase separation of extractants were investigated, the experimental results were shown in Fig. 9 and Fig.10.

Fig. 9 The influence of anti-nitration reagents on the phase separation performance of aldoxime
Fig. 10 The influence of anti-nitration reagents on the phase separation performance of mixture of aldoxime and ketoxime The data in Fig.9 and Fig.10 show that, the addition of anti-nitration reagent has little effect on the phase separation of extractants. AN1 has no effect on the extraction and strip phase separation of aldoxime or mixture of aldoxime and ketoxime, AN2 has a little effect on the phase separation of extractants, can slightly slow it. 2.2.2.2 The influence of anti-nitration reagents on the extraction performance The organic(10%,v/v) and standard feed (Cu2+:6g/L ， Fe3+: 3g/L， pH=2.0) were mixed at O/A=1:1, the influence of AN1 or AN2 on the extraction ability, extraction kinetics and Cu/Fe selectivity of aldoxime, TXIB modified aldoxime and mixture of aldoxime and ketoxime were investigated, the experimental results were shown in Table 4, Table 5 and Table 6. Table 4 The influence of anti-nitration reagents on the extraction performance of aldoxime Parameters Aldoxime Aldoxime+AN1 Aldoxime +AN2

Maximum Copper Loading Extraction Kinetics Cu/Fe Selectivity
5.99g/L 99.1% 3950
6.06g/L 99.0% 3240
6.09g/L 99.8% 3170
Table 5 The influence of anti-nitration reagents on the extraction performance of TXIB modified aldoxime Aldoxime Aldoxime+ Aldoxime+ Parameters +TXIB TXIB+AN1 TXIB+AN2 Maximum Copper Loading 5.95g/L 5.98g/L 6.02g/L Extraction Kinetics 98.1% 97.6% 97.1% Cu/Fe Selectivity 3050 2910 2830 Table 6 The influence of anti-nitration reagents on the extraction performance of mixture of aldoxime and ketoxime Parameters Maximum Copper Loading Extraction Kinetics Cu/Fe Selectivity Aldoxime +Ketoxime 5.40g/L 97.4% 3030 Aldoxime+ Ketoxime+AN1 5.42g/L 97.2% 2880 Aldoxime+ Ketoxime+AN2 5.45g/L 96.9% 2790
The data in Table 4,5 and 6 show that, AN1 or AN2 has no effect on the extraction ability and extraction kinetics of above extractants. AN1 or AN2 has a certain effect on the Cu/Fe selectivity of each extractant, among them relatively more effect on aldoxime , and limited effect on TXIB modified aldoxime and mixture of aldoxime and ketoxime. In general, the addition of anti-nitration reagent will not change the physical properties and the extraction ability of the extractant. 2.3 The measures for reducing the nitration of the extractants 2.3.1 Use stable extractants 2.3.1.1 Use ketoxime The experimental results showed that the anti-nitration ability of ketoxime was stronger than aldoxime. The nitration or degradation rate of ketoxime was slower than aldoxime in the same running condition. So it has advantage to use ketoxime or formulation extractants with higher contant of ketoxime to reduce the degradation and nitration of the extractants. 2.3.1.2 Use extractants containing anti-nitration reagents Use extrctants containing anti-nitration reagents can reduce the nitration and degradation of the extractants. While there may be some problems for the phase separation due to the anti-nitration reagents. Especially for a long time of running, the anti-nitration reagents and its degradation products can be accumulated in the extraction system and cause many phase separation problems. 2.3.2 Control the feed acidity When pH of feed is greater than 2.0, even though the nitrate concentration is 30g/L，the nitration speed of extractant is slow. If pH is greater than 2.3, the nitration speed would be slower. When the nitrate concentration in feed is higher, should control the pH greater than 2.3, in order to reduce the nitration of extractant.

2.3.3 Control the nitrate concentration in feed and strip solution To reduce the nitration of extractant, the nitrate concentration in feed should be controlled below 10g/L, preferably less than 5 g/L. As the acidity of strip solution is relatively higher, the concentration of NO3- should be controlled below 0.5 g/L. If the nitrate concentration in feed or strip solution is too high, the nitrate can be extracted by extraction method, the commonly used extractant is tri octyl/decyl amine. 2.3.4 Strengthen the scrub of loaded organic The nitration speed of extractant is greatly influenced by the acidity of system, the higher the acidity, the faster the nitration speed. Commonly, pH of feed is 1.5～2.0, the acidity is relatively low, the nitration speed is relatively slow. But the concentration of sulfuric acid in strip solution is commonly 180~200 g/L , if nitrate is brought into electrolyte by organic entrainment, even in low concentration can also lead to rapid degradation of extractant. So for the feed with high nitrate content, the loaded organic should be scrubbed adequately to reduce or avoid the entrainment of nitrate. 2.3.5 Reduce the acidity of strip reagent During the operation, organic will degrade and generate impurities， those impurities mostly have surface activity, can lead to slower phase separation and more entrainment. If the loaded organic is not scrubbed adequately, nitrate will be entrained into the strip solution, so the acidity of strip reagent should be reduced as low as possible on the premise that assures strip efficiency. 2.3.6 Add buffer agents to reduce raffinate pH value After the extraction of copper, the pH value of feed will drop, the addition of buffer agents such as sodium sulfate, sodium sulfite to feed ,to a certain extent, can buffer the reduction of feed pH. 3. Conclusion （1）The influence factors on the nitration of copper extractants include the types of extractant, acidity of feed or strip solution, nitrate concentration and the running temperature of extractants. Ketoxime and extractant with higher content of ketoxime have relatively stronger anti-nitration ability. The higer the acidity of feed, nitrate concentration and running temperature, the faster the nitration speed, on the contrary, the slower the nitration speed. （2） The addition of anti-nitration reagent AN1or AN2 will not change the physical properties and the extraction ability of the extractant, but can significantly improve the anti-nitration ability of extractants. （3）Use stable extractant, control the acidity of feed and strip reagent, reduce the nitrate concentration of system, strengthen the scrub of loaded organic , or add buffer agents to feed, these measures can reduce the nitration of extractant.
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