SMELTING POLYMETALLIC COPPER ORES

Transcription

1 Alloys of Copper SMELTING POLYMETALLIC COPPER ORES Ancient miners first utilized the oxidized secondary ores of copper to produce earliest extracted metals. They also came across rich deposits of primary copper ores in areas where erosion has exposed them at the surface. They were able to overcome the difficulty of extracting copper from sulfide ores. Finally they came across polymetallic ores of copper that may contain arsenic, antimony, zinc and lead together with iron. These were Fahlerz type ores form at lower levels of copper deposits. FAHLERZ TYPE ORES Major copper deposits may contain arsenic and antimony as impurity. During the weathering of such ores, arsenic and antimony is collected in the secondary enrichment zone together with chalcosite (Cu 2 S) and will forms minerals such as: Tetrahedrite: ((CuFe) 12 Sb 4 S 13 ) Tennantite: ((CuFe) 12 As 4 S 13 ) FORMATION OF SECONDARY ORES 1

2 APPEARENCE OF Cu-As ALLOYS EARLIEST Cu-As ALLOYS Nahal Nishmar Arslantepe Ikiztepe NAHAL MISHMAR 2

3 CHEMICAL ANALYSIS RESULTS OF NAHAL MISHMAR SAMPLES METHODS OF PREPARING Cu- As ALLOYS Sample Macehead Macehead Macehead Macehead Macehead Macehead No % Cu % As % Sb % Ni % Bi Tr Direct reduction Co-smelting Cementation Macehead Standard , Crown DIRECT SMELTING When the primary copper ores that contain arsenic (Copper sulpharsenide) are roasted they will turn into copper arsenate (olivenite). CuAsS + O 2 CuAsO 4 + CuO + As 2 O 3 + SO 2 Reduction of cupper arsenate by charcoal will yield Cu-As alloy CuAsO 4 + CO Cu-As (alloy) + CO 2 (olivenite) During roasting over 50% of arsenic is lost as As 2 O 3. Reactions are not balanced. CO-SMELTING Secondary copper ores are smelted together with sulfidic ores of arsenic. CuCO 3 + Cu 3 AsS 4 Cu-As + SO 2 + CO 2 enargite + FeAsS + FeO + SO 2 + CO 2 Arsenopyrite + As 2 S 3 + SO 2 + CO 2 Orpiment Charcoal is not necessary in this experiment because CO is not needed for reduction. Reactions are not balanced 3

4 CEMENTATION A mixture of arsenic ores such as Cu 3 AsS 4, FeAsS or As 2 S 3 with charcoal powder is added on to molten copper metal in a crucible. Arsenic is quickly reduced and incorporated into copper. REPLICA OF İKİZTEPE CRUCIBLE USING BOWL FURNACE ADDING ARSENIC ON MOLTEN COPPER 4

5 ARSENICAL COPPER METALLIC ARSENIC AT THE STEM OF FUNNEL PREPARATION OF ARSENICAL COPPER % Cu % As % Fe % S Experiment (70.3) 9.95 (13.6) 5.82 (5.18) 1.75 Experiment (90.0) 5.08 (10.1) 3.99 (3.34) 1.61 Experiment (86.8) 5.82 (7.31) 3.95 (3.45) 1.38 Experiment 4*96.3 (87.0) 2.08 (2.50) 0.43 (1.00) 1.13 Values in parenthesis are atomic absorption results, * Copper metal and arsenopyrite are heated together 5

6 ADVANTAGES OF CU-AS ALLOYS Copper that contains about 5% arsenic melts about 150 o C lower temperature. Thus, casting becomes much easier and better products are produced. Copper that contains 4% arsenic can be hot or cold forged much easier. When 4% arsenic containing copper is 50 % worked hardened it becomes nearly 50 % harder than pure copper. Arsenic retards the corrosion of copper objects. Copper that contains over 9% arsenic attains a silvery color Region where Cu and As forms Solid solution Cu-As PHASE DIAGRAM HARDNESS OF Cu- As ALLOYS HOROZTEPE BULL 6

7 Presently at the Boston Museum of Fine arts Made by Hattian metal smiths around 2100 BC. The bulk of the bull metal is bronz with less than % arsenic. There is a 10µ layer of arsenic rich layer of domeykite (Cu 3 As) which contain about 28% arsenic and gives the bull its silvery color. Domeykite layer is produced by cementation. In this method the bronze bull is heated in a mixture of As 2 O 3, K 2CO 3 and charcoal at C for some time. The reduced arsenic diffuse into copper in the solid form. ARSLANTEPE 7

8 Cu-As ARTIFACTS METAL ARTIFACTS FROM ROYAL TOMB İKİZTEPE 8

9 İKİZTEPE SPEARHEAD WITH DECORATION IKIZTEPE DIADEMS SPEARHEAD WITH FIGURINE (I/80-494) ANALYZED IKIZTEPE METAL ARTIFACTS Weapons Tools Jewellery Symbols Spearhead 147 Piercer 35 Bracelet 28 Emblem 16 Dagger 27 Flat axe 5 Earring 16 Pendant 6 Arrowhead 3 Blade 13 Spiral 10 I/ % Cu 86,4 % As 9.52 % Ni 0.15 % Zn 0.05 % Fe 0.09 % Sb 0.07 Chisel Other 6 20 Pin Anklet Other Total

10 ARSENIC CONCENTRATION OF IKIZTEPE METALS ACCORDING TO PERIODS % As As % ARSENIC CONCENTRATION ACCORDING TO TYPES LC EB I EB II EB III MB I 0 Weapons Tools Jewellery Symbols DISTRIBUTION OR ARSENIC CONCENTRATION IN IKIZTEPE OBJECTS As-Mass DISTRIBUTION OF IKIZTEPE SPEARHEADS Number of Samples < >10 As % As (%) Mass (gr) 10

11 IKIZTEPE CRUCIBLES STRABO S S ANATOLIAN MAP LOCATION OF IKIZTEPE ARSENIC SOURCES FOR IKIZTEPE METALURGISTS 11

12 DURAGAN ARSENIC SOURCE Tavşandağ Bakırçay valley Realgar and Orpiment ores: AsS and As 2 S 3 TAVSANDAG ARSENOPYRITE DEPOSIT SMELTING POLYMETALLIC COPPER ORES (Laboratory Experiments) Arsenopyrite: AsFeS 12

13 ORE DEPOSITS OF TAVSANDAG MERZIFON BAKIRÇAY COPPER DEPOSITS CHEMICAL ANALYSIS OF BAKIRÇAY SLAGS Sample Cu Pb Fe Zn As Sb Ag Ni Bi Co 95/ / / ,01 95/ /

14 BAKIRÇAY SLAGS METALLIC PRILL FROM BAKIRÇAY Chemical Composition: Cu: 56.2 % Pb: 19.2% Fe: 5.07% Sb: 6.86% Zn: 4.69% As: 5.77% BAKIRÇAY POLYMETALLIC ORES CHEMICAL ANALYSIS OF SMELTING CHARGE Cu Pb Fe Zn As Sb Roasted nd Unroasted nd Speiss

15 BAKIRÇAY CHALCOPYRITE AND SMELTED METAL BOWL FURNACE FOR SMELTING CHEMICAL ANALYSIS OF PRILLS FROM SMELTING EXPERIMENTS Element Range (%) Average (%) Cu Pb Fe Zn As -8, WHY Cu-As ALLOYS WERE ABANDONED Roasting of sulfide ores with arsenic caused arsenic to be lost as a sublimate Due to the volatility of arsenic, its composition in copper could not be easily controlled. The availability of recognizable arsenic rich ores were limited Toxic effect of arsenic was detrimental to the health of the smith. 15