Mark Stevenson Ecobat Technologies

Transcription

1 Mark Stevenson Ecobat Technologies

2 Secondary Lead 50 years ago The history of secondary lead and its operations are quite different to those of the primaries In many countries it was just been considered part of the scrap industry where the material is melted and inferior to secondary Many of the companies history linked back to the owner being a battery manufacturer or part of the scrap metal industry Plants were quite basic; small blast or rotary furnaces often used

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4 Secondary Lead Now Not much has changed for many areas!!! Whilst there has been much consolidation and improvement in many countries, such as the USA and Europe, in other parts the scene resembles operations and conditions of 50 years ago Particularly through Asia where many new smelters are beginning to operate due to the low cost of entry into the market

5 Secondary Lead Now Off the shelf plants can be easily purchased and be operating quite quickly, but often in a crude mode Basically we are using the same equipment of 50 years ago! But long established plants operating in some countries are under enormous pressure to adhere to ever tightening regulations i.e. pollution control, slags etc. There is no level playing field for secondary lead

6 Secondary Lead Technically Unfortunately secondary lead is often dismissed technically because of its simplicity and small scale of operation But, in my opinion, it is more complex metallurgically than primary smelting!!! Whilst it does seem basic, there has been a lot of improvement, or more aptly termed, adjustment to the operations in terms of slags, refractories, furnace design etc. over the past 50 years So why are some operators in crude mode?

7 The Soda-Iron System New entrants to the market use this very basic, but complex system for smelting; Basic slag forming materials readily available Low melting point Easily worked But these slags have been banned in many western countries, forcing operators there to produce more complex oxide slag s and change downstream processing; end result a more environmentally stable waste product

8 The Soda-Iron System The slag is based in the sulphide matrix system, which is uncommon in metallurgical operations Fe and C react with the PbSO 4 producing lead metal via the following; PbSO 4 + C PbS + CO 2 then PbS + Fe Pb + FeS This reaction is often used to describe the slag, but it is only one of many hundreds of reactions occurring

9 Liquid + Solid Liquid + Solid

10 Operating Zone ~ o C Liquid + Solid Liquid + Solid

11 Element Capture There are a whole host of other elements and compounds in typical battery scrap: From plates Sb, As, Sn, Ca, Cd, Al, Cu, Ba From separators/plastics SiO2, Al2O3, Cl, Br From refractories and other sources Cr, Mn, Nicad s The slag easily absorbs these elements into the matrix and encapsulating them into various compounds

12 Element Capture But the major problem element is sulphur Over 99.5% is captured in the slag No auxiliary equipment is needed to capture the element Wet scrubbers Acid plants Absorbent beds There are some small peaks during smelting, such as acid decomposition, but the overall stack emission is below 100 ppm

13 Uncontrolled Smelting The system has a large tolerance for errors! This allows the new (and old) players to the market just to copy and guess the amount of additives required; Poor quality iron (oxidized) and coke Not to the correct levels or ratios Other compounds that are not needed which, more often than not, has a detrimental effect on the slag system

14 Uncontrolled Smelting These variances to the system has a huge impact on the operation, performance and environmental output of the furnace; Poor capture of sulphur > high emissions High lead in slag, upwards of 12 to 15% Higher operating temperatures Erosion of refractories etc, etc, Uncontrolled smelting = Uncontrolled operations

15 If you look after the slag, the metal looks after itself

16 An Idea into Reality Outlined in the upcoming slides is an idea, developed though observations and experience, that challenges current lead smelting practices. It proposes a paradigm shift in operations and thinking, one which could potentially lead to a secondary lead plant that produces no solid waste

17 Observations and Ideas In operating the soda-iron system it is not uncommon to observe different phases/products now & then Two of the major products observed are; Black dense phase seemingly high in Pb Bright green phase that does not break down during storage Crystalline white and dark phases Metallic type phases Often it quite hard to understand how these products are formed and under what conditions due to batch operations of the plant

18 Ideas and Experiments The system is not that complex There are only four major ingredients to a batch Lead bearing feed Coke/Coal Soda Ash Iron Flexibility of the rotary furnace and being a batch process will allow monitoring and analysis of the output products

19 Ideas and Experiments Further detailed examination of these odd products revealed two major phases A black phase high in PbS (and Fe) A white phase predominantly Na 2 SO 4 Aim was to mimic these reactions in a controlled state understanding and monitoring the conditions involve The experimental program was set up to conduct the tests in a 15 tonne rotary furnace, under normal operating conditions over four charges. (No laboratory tests would be undertaken!)

20 Iron Initial Test Matrix Tap C = 300 Fe = 1400 Pb(slag) = 10% Normal Tap C = 600 Fe = 1400 Pb(slag) ~ 4% Tap C = 300 Fe = 400 Pb(slag) = 23% Tap C = 600 Fe = 700 Pb(slag) = 14% Tap C = 600 Fe = 400 Pb(slag) = 60% Anthracite

21 The Aim was Achieved! From the first set of tests it was clear that there were other systems under controlled operations that could be produced The three products were envisioned; PbS rich matte, a product that is acceptable for primary smelters Crude Na 2 SO 4 that can be processed to produce a pure product for sale Bullion lead, as per normal operations And no slag.

22 Cast Iron Borings 1600 Lead in Slag Current Smelting Area Pb ~ 4% Anthracite

23 Cast Iron Borings Lead in Slag Current Smelting Area Pb ~ 4% Anthracite

24 Cast Iron Borings Lead in Slag 10 Current Smelting Area Pb ~ 4% Anthracite

25 The Results Four major phases present; alpha phase; very high lead, 70-80% Silver, dense Most metal elements reporting here Green beta phase Elevated lead 25 35%, with high Fe up to 20% Lighter green than erdite zoned from alpha phase Some elements report especially SiO 2

26 The Results soda phase; Erdite Predominately high Na 2 SO 4, over 90% Distinct layer on top of alpha/beta phase Much lighter density than other phases Low level of elements reporting other than As Still present in some batches

27 The α phase

28 Cast Iron Borings Lead in Slag 10 Current Smelting Area Pb ~ 4% Anthracite

29 90 80 wt%pb iron carbon

30 iron carbon wt%pb

31 Slag iron Matte carbon wt%pb

32 Immiscibility Gap Sn Pb SO 4 (Soda Phase) Fe Ni Oxide (β phase) SiO2 Sulphide (α phase) Cu As Sb

33 Immiscibility Wonderful Phenomena Alpha Soda Lead Iron Arsenic Sodium Tin Antimony Copper Cadmium 0.03 <0.001 Zinc/Nickel 0.04 <0.001 All values in percent

34 Supporting Theory - Iron Low Fe > PbS formation High Fe > Erdite formation Iron levels drive the formation of the lead sulphide: simply because it is not available for erdite formation Sodium does not seem to have an affinity for a lone sulphide phase without iron present

35 Why? We are limiting the sulphate to sulphide reaction; PbSO 4 + C PbS + CO 2 then PbS + Fe Pb + FeS

36 Supporting Theory - Carbon Low C > High Na 2 SO 4 High C > Limited Na 2 SO 4 Carbon is linked to the formation of PbS via; PbSO 4 + C PbS + CO/CO 2 Limit carbon and the reported secondary reaction takes place; PbSO 4 + Na 2 CO 3 PbO + Na 2 SO 4

37 Outputs Matte can be processed as is High sulphate levels Heavy Sulphate Penalty applied Product can be washed with the sulphate removed Upgrading PbS to around 85% Pseudo concentrate Clean Na 2 SO 4 produced

38 10 min 45 min 100 min 150 min

39 Matte Water Leach Treatment Route To Furnace Crush Solids (Lead, C & Iron) O/S wash liquor Slurry Screen U/S filter liquor Neut. tanks solids Primary Smelter Na2SO4 Crystallizer

40 ppm insolution Fe Sn 60 Sb ph

41 Desulphurization in the Furnace! Soda as is Dissolved ph treated (%) (ppm) (ppm) Lead 0.35 <1 <1 Iron 0.16 <1 <1 Arsenic <1 Sodium 35+ Tin <1 Antimony <1 Copper <1 <1 Cadmium <0.001 <1 <1 Zinc/Nickel <0.001 <1 <1

42 To the Point.. The idea works! 600+ charges were carried out over a total 3 month period 281 charges run end-to-end Test-work was done in the furnace, no bench tests No metallurgical/phase variability i.e repeatable Lead recovery 99.99%+; no disposable residue No adverse effect to the refractory

43 Secondary Lead - Future Secondary lead faces an image problem both real and imagined in some areas going into the future; Poor quality/high impurities Scrap based recycled product Inferior to Primary In other areas it is seen as a quality product! We have to correct the playing field to make it more even

44 Secondary Lead - Future We have to produce to a common standard ; Commercially Technically Environmentally There has to be a phase shift in some countries to catch up and produce to a world standard We have to step up and be counted!

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