Synthesis and Solubility of Arsenic Tri-sulfide and Sodium Arsenic Oxy-sulfide Complexes in Alkaline Sulfide Solutions by Wen Li B. Sc., (Materials Engineering), Hebei University of Technology, China, 2006 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE STUDIES (Materials Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) June 2013 © Wen Li, 2013 Abstract Alkaline sulfide leaching (ASL) at approximately 100 ºC has been used to selectively extract arsenic and antimony from enargite and tetrahedrite concentrates. Sodium thio- arsenate has been postulated to crystallize from alkaline sulfide leaching solutions upon cooling. However, literature data on the solubility of sodium thio-arsenate as well as proof of its crystallization from ASL solutions is scant. In this thesis, the solubility of leach-produced and synthetic sodium thio-arsenate is studied. To determine arsenic solubility in ASL solutions, sodium thio-arsenate and sodium arsenic oxide sulfide complexes are synthesized by various means and characterized by EDX, QXRD, and ICP. The synthesis of amorphous As S , sodium arsenic oxy-sulfide complexes, and 2 3 sodium thio-arsenate is first presented. For amorphous As S synthesis, the effect of 2 3 concentration of sodium sulfide (0.1 M) and hydrochloric acid (1 M), temperature (40 ~ 60 ºC), and aging time (48 hours) was optimized. The solubility of synthetic sodium arsenic oxy-sulfide complexes and sodium thio-arsenate in ASL solutions increases significantly as temperature is increased to 95 ºC. More importantly, the solubility of sodium thio-arsenate at certain temperatures is significantly affected by the concentration of sodium hydroxide and sulfide in solution. Due to the common ion effect, if NaOH and HS- concentrations are very high, the solubility of sodium thio-arsenate decreases. Enargite leaching tests were done to characterize the precipitate that occurred upon cooling and to verify the arsenic saturation point, which should be between 38.5 ~ 58 g/L (0.51 M ~ 0.78 M) As depending on the NaOH and HS- concentration. Comparison with i solubility experiments of pure sodium thio-arsenate shows that arsenic solubility in ASL solutions is supersaturated. However, direct comparison of saturation in ASL solutions and the solubility as obtained by the synthetic solutions/crystallites prepared here is not possible given the complex nature of the ASL crystallites that appear not to contain the often discussed “sodium thio-arsenate”. ii Preface This dissertation is original, unpublished, independent work by the author, W. Li. iii Table of Contents Abstract ..................................................................................................................................................................i Preface ................................................................................................................................................................. iii Table of Contents .................................................................................................................................................iv List of Tables ..................................................................................................................................................... viii List of Figures ....................................................................................................................................................... x Acknowledgments .............................................................................................................................................. xiv Chapter 1 Introduction ........................................................................................................................................ 1 Chapter 2 Literature Review ............................................................................................................................... 7 2.1 Copper arsenic minerals ............................................................................................................................... 7 2.2 Metallurgical processing of enargite .......................................................................................................... 11 2.2.1 Pyrometallurgical treatment ............................................................................................................... 14 2.2.2 Alkaline sulfide leaching of enargite .................................................................................................. 17 2.2.3 Arsenic removal and precipitate analysis ........................................................................................... 20 2.2.4 Sodium thio-arsenate solubility .......................................................................................................... 24 2.3 Synthesis of amorphous As2S3 ................................................................................................................... 25 2.4 Synthesis of sodium thio-arsenate .............................................................................................................. 26 2.5 Solubility of amorphous As2S3 ................................................................................................................... 30 Chapter 3 Objectives .......................................................................................................................................... 33 Chapter 4 Experimental Procedures ................................................................................................................ 34 4.1 Preliminary solubility study on arsenic trioxide ......................................................................................... 34 4.2 Synthesis of amorphous As2S3 ................................................................................................................... 34 4.2.1 Concentration effect ............................................................................................................................ 37 4.2.2 Temperature effect .............................................................................................................................. 39 4.2.3 Effect of hydrochloric acid addition rate ............................................................................................ 39 4.2.4 Aging time effect ................................................................................................................................. 40 4.3 Solubility of amorphous As2S3 in sodium sulfide solution ......................................................................... 40 iv 4.4 Synthesis of sodium thio-arsenate .............................................................................................................. 40 4.4.1 Synthesis of precursor sodium arsenate by hydrogen peroxide oxidation of As (III) ......................... 40 4.4.1.1 Synthesis of sodium thio-arsenate from sodium arsenate and sodium sulfide solution ................................ 42 4.4.1.2 Synthesis of sodium thio-arsenate from sodium arsenate and solid sodium sulfide ..................................... 42 4.4.1.3 Synthesis of sodium thio-arsenate from sodium arsenate and hydrogen sulfide gas ..................................... 43 4.4.2 Synthesis of sodium thio-arsenate by reaction of arsenic tri-sulfide with elemental sulfur ................ 45 4.5 Solubility of synthetic sodium arsenic oxy-sulfide complexes and sodium thio-arsenate .......................... 46 4.6 Solubility accuracy calibration test ............................................................................................................ 47 4.7 Precipitation from an enargite leaching test ............................................................................................... 48 Chapter 5 Results and Discussion ..................................................................................................................... 52 5.1 Solubility of As2O3 in Na2S and NaOH solution ........................................................................................ 52 5.2 Characterization of synthesized amorphous As2S3 ..................................................................................... 55 5.2.1 Effect of reagent concentrations ......................................................................................................... 56 5.2.2 Effect of temperature .......................................................................................................................... 57 5.2.3 Effect of hydrochloric acid solution flow rate..................................................................................... 59 5.2.4 Effect of aging time ............................................................................................................................. 60 5.3 Solubility of As2S3 in Na2S solution........................................................................................................... 61 5.4 Characterization of synthetic crystalline products ...................................................................................... 63 5.4.1 Attempts to synthesize sodium arsenic oxy-sulfide from sodium arsenate precursor ......................... 63 5.4.2 Synthesis of sodium thioarsenate by reaction of As S with elemental sulfur ..................................... 67 2 3 5.4.3 Arsenic content determination by ICP analysis .................................................................................. 69 5.5 Solubility of synthesized sodium thio-arsenate products ........................................................................... 70 5.5.1 Sodium arsenate precursor synthesized by oxidation of As (III) with hydrogen peroxide .................. 70 5.5.1.1 Sodium thio-arsenate synthesized by the addition of sodium sulfide solution to dissolved sodium arsenate precursor (product #1) .............................................................................................................................................. 70 5.5.1.2 Sodium thio-arsenate synthesized by the addition of solid sodium sulfide to dissolved sodium arsenate precursor (product #2) .............................................................................................................................................. 70 5.5.1.3 Sodium thio-arsenate synthesized by the addition of hydrogen sulfide to dissolved sodium arsenate precursor (product #3) .............................................................................................................................................. 72 5.5.2 Synthesis of thio-arsenate by oxidation of As (III) with elemental sulfur ........................................... 73 v 5.5.2.1 Solubility of sodium thio-arsenate (product #4) in leach solution under air atmosphere and argon atmosphere ............................................................................................................................................................... 73 5.5.2.3 Solubility of synthetic crystal #4 (sodium thio-arsenate) at constant hydroxide (2.5 M/100 g/L) and varying hydrosulfide content (0 M ~ 1.0 M/0 ~ 56 g/L) in argon .......................................................................................... 75 5.6 Solubility accuracy calibration test ............................................................................................................ 78 5.7 Solubility of As in ASL solutions originating from an enargite leaching test ............................................ 78 Chapter 6 Conclusion ......................................................................................................................................... 82 Chapter 7 Future Work ..................................................................................................................................... 83 References ........................................................................................................................................................... 84 Appendix ............................................................................................................................................................. 90 Part A. Tables of solubility data by experiment and OLI systems software for amorphous As S and synthetic 2 3 crystals ............................................................................................................................................................. 90 A.1 Solubility data of orpiment in literature and amorphous As S by experiment and OLI systems 2 3 software ....................................................................................................................................................... 90 A.2 Solubility data of synthetic crystal #2, #3, #4 (sodium thio-arsenate) by experiment ........................... 96 A.2.1 Solubility of synthetic crystal #2 in air ........................................................................................................... 96 1. In 100 ml 2.5 M sodium hydroxide and 1.0 M sodium sulfide solution ..................................................... 96 2. In 100 ml 2.5 M sodium hydroxide and 0.5 M sodium sulfide solution ..................................................... 96 3. In 100 ml 1.0 M sodium hydroxide and 1.0 M sodium sulfide solution ..................................................... 96 A.2.2 Solubility of synthetic crystal #3 in air ........................................................................................................... 97 1. In 10 ml 2.5 M sodium hydroxide and 1.0 M sodium sulfide solution....................................................... 97 2. In 10 ml 2.5 M sodium hydroxide and 0.5 M sodium sulfide solution....................................................... 97 3. In 10 ml 1.0 M sodium hydroxide and 1.0 M sodium sulfide solution....................................................... 98 A.2.3 Solubility of synthetic crystal #4 (sodium thio-arsenate) in air ...................................................................... 98 1. In 20 ml 2.5 M sodium hydroxide and 1.0 M sodium sulfide solution under air atmosphere .................... 98 2. In 20 ml 2.5 M sodium hydroxide and 0.5 M sodium sulfide solution under air atmosphere .................... 98 3. In 20 ml 1.0 M sodium hydroxide and 1.0 M sodium sulfide solution under air atmosphere .................... 99 A.2.4 Solubility of synthetic crystal #4 (sodium thio-arsenate) in argon .................................................................. 99 1. In 10 ml 2.5 M sodium hydroxide and 1.0 M sodium sulfide solution under argon atmosphere ............... 99 vi 2. In 10 ml 2.5 M sodium hydroxide and 0.5 M sodium sulfide solution under air atmosphere .................. 100 3. In 10 ml 1.0 M sodium hydroxide and 1.0 M sodium sulfide solution under air atmosphere .................. 100 A.2.5 Solubility of synthetic crystal #4 (sodium thio-arsenate) at constant hydroxide and varying hydrosulfide content in argon ...................................................................................................................................................... 101 1. In 10 ml 2.5 M sodium hydroxide and 1.0 M sodium hydrosulfide solution ........................................... 101 2. In 10 ml 2.5 M sodium hydroxide and 0.5 M sodium hydrosulfide solution ........................................... 101 3. In 10 ml 2.5 M sodium hydroxide and 0 M sodium hydrosulfide solution .............................................. 101 Part B. EDX analysis of synthetic complexes ................................................................................................ 102 Part C. Quantitative x-ray diffraction result of arsenic precipitate from enargite leaching ............................ 105 vii List of Tables TABLE 1.1 MAJOR ARSENIC MINERALS OCCURRING IN NATURE (WTO ARSENIC COMPOUNDS, 2001) .................... 1 TABLE 1.2 ARSENIC DEPOSITS OF THE WORLD (WTO ARSENIC COMPOUNDS, 2001) .............................................. 2 TABLE 1.3 SUMMARY OF TOXIC EFFECTS IN HUMANS AFTER OCCUPATIONAL INHALATION EXPOSURE TO INORGANIC ARSENIC COMPOUNDS (EUROPEAN COMMISSION 2001) ............................................................... 4 TABLE 2.1 THE MOST COMMONLY FOUND (OR ANTICIPATED) ARSENIC COMPOUNDS IN AIR (EUROPEAN COMMISSION 2001) ........................................................................................................................................ 8 TABLE 2.2 THE MOST COMMON CU-AS-SB-S MINERALS AND THEIR PHYSICAL PROPERTIES (BARTHELMY 2004) ... 9 TABLE 4.1 CONDITIONS OF AS2S3 SYNTHESIS CONCENTRATION TESTS .................................................................. 37 TABLE 4.2 CONDITIONS OF AS2S3 SYNTHESIS TEMPERATURE TESTS ...................................................................... 39 TABLE 4.3 CONDITIONS OF AS2S3 SYNTHESIS FLOW RATE TESTS ........................................................................... 39 TABLE 4.4 CONDITIONS OF AS2S3 SYNTHESIS AGING TIME TESTS .......................................................................... 40 TABLE 4.5 THREE DIFFERENT LEACH SOLUTIONS FOR SOLUBILITY TESTS.............................................................. 47 TABLE 4.6 THREE CONDITIONS FOR VARYING HYDROSULFIDE AND CONSTANT NAOH ......................................... 47 TABLE 4.7 ELEMENTAL ANALYSIS OF THE ENARGITE SAMPLE ............................................................................... 49 TABLE 4.8 QUANTITATIVE PHASE ANALYSIS OF THE ENARGITE SAMPLE ............................................................... 49 TABLE 5.1 EDX RESULT FOR EFFECT OF CONCENTRATION .................................................................................... 56 TABLE 5.2 EDX RESULT FOR EFFECT OF TEMPERATURE ........................................................................................ 58 TABLE 5.3 EDX RESULT FOR EFFECT OF HYDROCHLORIC ACID FLOW RATE .......................................................... 59 TABLE 5.4 EDX RESULT FOR EFFECT OF AGING TIME ............................................................................................ 60 TABLE 5.5 ELEMENTAL ANALYSIS OF SYNTHETIC SODIUM ARSENATE BY EDX .................................................... 63 TABLE 5.6 EDX ANALYSIS FOR SYNTHETIC CRYSTAL #1, #2, AND #3 ................................................................... 64 TABLE 5.7 ELEMENTAL ANALYSIS OF SYNTHETIC CRYSTALLINE PRECIPITATE #4 BY EDX ................................... 67 TABLE 5.8 QXRD RESULT AND CRYSTAL PARAMETERS OF SYNTHETIC SODIUM THIO-ARSENATE ......................... 67 TABLE 5.9 ICP ANALYSIS FOR ARSENIC CONTENT IN PRECIPITATES #2, 3 AND 4 ................................................... 69 TABLE 5.10 SOLUBILITY DATA FOR ACCURACY CALIBRATION .............................................................................. 78 TABLE 5.11 ARSENIC CONCENTRATION OF SOLUTION A. AND B. BY ICP ............................................................... 79 TABLE 5.12 QXRD RESULT FOR ARSENIC PRECIPITATE FROM ENARGITE LEACHING TESTS (SEE XRD SPECTRA IN APPENDIX FIGURE C-1, 2, 3)......................................................................................................................... 80 TABLE A-1 ORPIMENT SOLUBILITY IN SOLUTIONS TO WHICH NO SULFIDE HAS BEEN ADDED (WEBSTER 1990) ..... 90 TABLE A-2 ORPIMENT SOLUBILITY IN SOLUTIONS TO WHICH SULFIDE HAS BEEN ADDED (WEBSTER 1990) .......... 91 viii TABLE A-3 SOLUBILITY PREDICTION OF AS2S3 IN 1 WT% OF 1 L NA2S SOLUTION ................................................. 93 TABLE A-4 SOLUBILITY PREDICTION OF AS2S3 IN 2 WT% OF 1 L NA2S SOLUTION ................................................. 94 TABLE A-5 SOLUBILITY PREDICTION OF AS2S3 IN 3 WT% OF 1 L NA2S SOLUTION ................................................. 95 TABLE A-6 SOLUBILITY OF AS2S3 IN 1 WT%, 2 WT%, AND 3 WT% OF 80 ML NA2S SOLUTION ............................... 95 TABLE A-7 SOLUBILITY OF IN 2.5 M NAOH AND 1.0 M NA2S SOLUTION .............................................................. 96 TABLE A-8 SOLUBILITY OF IN 2.5 M NAOH AND 0.5 M NA2S SOLUTION .............................................................. 96 TABLE A-9 SOLUBILITY OF IN 1.0 M NAOH AND 1.0 M NA2S SOLUTION .............................................................. 97 TABLE A-10 SOLUBILITY OF IN 2.5 M NAOH AND 1.0 M NA2S SOLUTION ............................................................ 97 TABLE A-11 SOLUBILITY OF IN 2.5 M NAOH AND 0.5 M NA2S SOLUTION ............................................................ 97 TABLE A-12 SOLUBILITY OF IN 1.0 M NAOH AND 1.0 M NA2S SOLUTION ............................................................ 98 TABLE A-13 SOLUBILITY OF NA3ASS4·8H2O IN 2.5 M NAOH AND 1.0 M NA2S SOLUTION .................................. 98 TABLE A-14 SOLUBILITY OF NA3ASS4·8H2O IN 2.5 M NAOH AND 0.5 M NA2S SOLUTION .................................. 99 TABLE A-15 SOLUBILITY OF NA3ASS4·8H2O IN 1.0 M NAOH AND 0.5 M NA2S SOLUTION .................................. 99 TABLE A-16 SOLUBILITY OF NA3ASS4·8H2O IN 2.5 M NAOH AND 1.0 M NA2S SOLUTION ................................ 100 TABLE A-17 SOLUBILITY OF NA3ASS4·8H2O IN 2.5 M NAOH AND 0.5 M NA2S SOLUTION ................................ 100 TABLE A-18 SOLUBILITY OF NA3ASS4·8H2O IN 1.0 M NAOH AND 0.5 M NA2S SOLUTION ................................ 100 TABLE A-19 SOLUBILITY OF NA3ASS4·8H2O IN 2.5 M NAOH AND 1.0 M NAHS SOLUTION .............................. 101 TABLE A-20 SOLUBILITY OF NA3ASS4·8H2O IN 2.5 M NAOH AND 0.5 M NAHS SOLUTION .............................. 101 TABLE A-21 SOLUBILITY OF NA3ASS4·8H2O IN 2.5 M NAOH AND 0 M NAHS SOLUTION ................................. 101 ix