Silver Recovery and the Responsible Darkroom

Spent fixer is the only liquid a darkroom produces that is worth money, and the only one that manufacturers on two continents agree must not reach a drain untreated. Both facts come from the same property: it holds dissolved silver, at a concentration nothing else in the house comes close to. This page works out how much of it there actually is at a domestic scale, sets out the four methods industry uses to take it back and what each one leaves you holding, and then asks the question the equipment catalogues never do — which of them survives contact with a house rather than a processing plant.

The answer to that last question is not the one a reader hoping to make money expects, and the reason it is not is worth more than the answer.

How much silver is in the bottle

Three numbers, from three directions, and they are not the same kind of statement.

Per litre, measured by the manufacturers. Kodak tabulates the overflow from a black-and-white fixer at 3,000 to 7,000 mg of silver per litre — three to seven grams in a litre — and colour fixers and bleach-fixes higher still, to 12,000 mg/L. Its guidance written for amateurs gives a narrower 3,000 to 5,000 mg/L for fixer and bleach-fix, negligible silver in developer, and 1 to 5 mg/L in wash water and stabiliser. The United States Environmental Protection Agency’s own guide for photo processors gives the whole range across every stream as less than 5 mg/L to 12,000 mg/L, and says what the silver is: predominantly the soluble silver-thiosulfate complex, with small amounts of silver sulfide.

Per film and per print, Part XI has already done the arithmetic and does not need it repeated. ILFORD’s two published limits — 24 rolls of 135-36 per litre, and a ceiling of 8 to 10 g/L — imply 0.33 to 0.42 g of silver per roll; Kodak’s coating weights imply less; and Part XI could not make the two routes meet, so the roll figure is a bracket whose upper end is what this page uses. An 8 × 10 fibre print sheds 50 mg, which falls out of two of ILFORD’s own statements and is the firmest single figure in the part.

Per year is the number nobody publishes, because it depends on you. It is also the only one that decides anything, so it is the one this page works.

🧮A year of silver, for a stated workflow

Take a photographer who exposes four rolls of 135-36 a month and makes twenty 8 × 10 fibre prints a month. Nothing about that is typical; it is stated so the arithmetic can be checked and so you can substitute your own log.

The mass.

(48 rolls × 0.33 to 0.42 g) + (240 prints × 0.05 g) = 16 to 20 g + 12 g ≈ 28 to 32 g

Silver reaching the fixer in a year

Call it of order 30 g of silver a year, and treat the film half as an upper bound, because Part XI’s other route implies less and the two were never reconciled. Notice that the prints contribute nearly as much as the films even though a print sheds under a seventh of what a roll does: volume of work, not richness of material, is what fills the bottle.

The liquid it is in. ILFORD publishes 24 films of 135-36 per litre unreplenished, so the film work makes 2 L of spent fixer. The print work is governed by a different limit: ILFORD’s ceiling for prints needing maximum stability is 0.5 g/L, which it says is about ten 8 × 10 fibre prints per litre, so 240 prints make 24 L. Held only to the commercial-permanence ceiling of 2 g/L — about forty prints per litre — the same work makes 6 L.

So print fixer, not film fixer, is what fills the waste container, by a factor of three to twelve, and it does so precisely because it was discarded early for permanence. The most careful printer produces the most waste. That is not a paradox; it is the cost of the standard.

What the concentrations then are. The film bath comes out at 8 to 10 g/L and the print bath at 0.5 g/L — both of which are ILFORD’s own ceilings, arrived at by construction rather than by measurement, because that is where the per-roll and per-print figures came from.

Be clear about which of those is evidence. The per-litre figures reproduce ILFORD’s own ceilings and are not independent checks on them. The one independent check available is Kodak’s: a hard-worked black-and-white bath at 3 to 7 g/L, from a different manufacturer measuring different machines, sits just below the film figure — consistent with Part XI’s conclusion that ILFORD’s capacity is set with margin. The genuinely new results here are the total mass and the total volume, and neither appears in any manufacturer’s sheet.

Why any of this matters

Take the average across everything the year produced: about 30 g of silver in something between 8 and 26 L, which is 1 to 4 g/L across the whole darkroom. Take the lower end of that, from the largest volume, because it is the most dilute way the year can honestly be stated.

Kodak’s disposal publication lists the parameters municipal sewer codes most often regulate, with their mean limits: biochemical oxygen demand 350 mg/L, suspended solids 200 mg/L, pH 5.6 to 9.4, silver 1.2 mg/L and iron 17 mg/L. Set the darkroom average against the silver figure.

1,150 mg/L ÷ 1.2 mg/L ≈ 960

How far over a mean sewer limit the most dilute whole-darkroom average sits

Take the fixer on its own, at Kodak’s 3,000 to 7,000 mg/L, and the ratio is between two and six thousand. Part II rounded that to “of order a thousand” and the rounding is the right one, because no end of the range changes the decision.

The hazard behind the limit is aquatic. The silver entries on the ECHA inventory carry H400, very toxic to aquatic life, and H410, very toxic to aquatic life with long lasting effects, with the environmental pictogram. In the United States a liquid waste at or above 5 ppm of silver is a characteristic hazardous waste, EPA number D011, and Kodak’s own regulatory sheet lists used fixers, bleach-fixes and low-flow washes among the solutions that typically exceed it — while recording that processed and unprocessed films and papers, tested by the leaching procedure, did not. Sheet and bath are two different waste questions, and the sheet is the easy one.

!Kodak says the silver in a fixer is not toxic. It also says recover it.

Two Kodak publications state, in as many words, that the form of silver in photographic effluent — the thiosulfate complex — is not toxic, and that it is removed during secondary treatment at a works. The amateur guidance goes further and says an amateur photographer, as a domestic user, is excluded from the pretreatment regulations that bind businesses.

The same publications then say to recover the silver anyway: because sewer codes regulate total silver rather than the species it is in, because recovery conserves a resource, and because it may return money.

Both halves are true and they are not in conflict, and the reason matters more than either. A hazard classification is written for a substance, a discharge limit is written for a stream, and a treatment works is a biological process with a limited tolerance. The complex is not the free ion, and free silver ion is what is acutely toxic to micro-organisms — Kodak says that too. But a limit expressed as total silver does not ask what the silver is bound to, and neither does the H410 on the silver entries, and neither does a sewer inspector. The course does not resolve the tension by picking the half it prefers. It states both, and keeps collecting, and says why below.

The four ways to get the silver back

Every practical method is one of four, and each produces a different physical object that a refiner then has to process. That last point is the one usually left out, and it is where the domestic answer comes from.

[Ag(S₂O₃)₂]³⁻ + e⁻ → Ag + 2 S₂O₃²⁻

Electrolysis, cathode: an electron reduces the complexed silver to the metal

SO₃²⁻ + H₂O → SO₄²⁻ + 2 H⁺ + 2 e⁻

Electrolysis, anode: sulfite gives up the electrons and becomes sulfate

Electrolysis passes a direct current between two electrodes; silver plates onto the cathode as metal and sulfite is oxidised at the anode, which is why a fixer loses preservative as it is desilvered. It is the method ILFORD recommends for maximum efficiency, because the treated fixer can be reused. Kodak states recovery above 90 per cent and a plate above 90 per cent silver. Its floor is the interesting part: post-cell concentrations are normally 200 to 800 mg/L, and pushing a cell below about 200 mg/L by longer residence or more current gives “an inferior, black, crumbly, silver-sulfide-contaminated plate” that drops the cell’s efficiency instead of raising it. ILFORD adds that vigorous electrolysis may release hydrogen sulfide. So electrolysis is a primary treatment that almost always needs something after it.

2 [Ag(S₂O₃)₂]³⁻ + Fe → 2 Ag + Fe²⁺ + 4 S₂O₃²⁻

Metallic replacement: iron reduces the silver in its complex and takes its place in solution

Metallic replacement is a jar of steel wool with a plumbing fitting on it. Iron is above silver in reactivity, so it hands over electrons and dissolves while silver comes out as a black solid that stays in the cartridge. Kodak states recovery above 95 per cent and, for a cartridge working properly, a final concentration below 5 mg/L — an order of magnitude better than electrolysis, from equipment costing two orders of magnitude less. The silver bromide entry carries the same reaction written for free silver ions, which is the case in a silver nitrate solution; the equation above is the one that applies in a fixer, where the silver is held in the second of Part III’s stepwise thiosulfate complexes.

The drawbacks are all practical rather than chemical. Dwell time is the single biggest factor, so flow rate has to be controlled. The steel channels as it is consumed, and silver can break through well before the iron is gone. The bath must be mildly acidic — Kodak’s cartridge sheet gives an ideal pH of 5.5 to 6.5, its small-volume disposal sheet a workable 4 to 6.5, and both agree on the failure modes at each end: below about pH 4 to 5 the steel dissolves too fast to be useful, above pH 7 the reaction is too slow. And the process discharges iron, which some sewer codes limit in their own right, at a mean of 17 mg/L.

Chemical precipitation throws the silver down as an insoluble solid. The classical reagent is a soluble sulfide, and it reaches the lowest concentrations of any method — but it is the one route the industry has walked away from. Overdose the sulfide and the excess leaves as hydrogen sulfide; Kodak requires an accurate silver measurement before dosing for exactly that reason, calls it a method for trained personnel at centralised facilities, and notes that the precipitate plugs filters. The EPA guide is blunter: processors no longer use sulfide, borohydride or amine borate precipitation because of the hazards. Kodak’s own replacement, a trimercaptotriazine reagent, is a proprietary two-part system reaching an average below 1.5 ppm.

Ion exchange is the only one of the four aimed at wash water rather than fixer. A resin swaps a chloride or sodium ion for the silver complex, and reaches 0.1 to 0.5 ppm; the EPA guide gives up to 98 per cent recovery and effluents as low as 0.1 ppm. It works on dilute solutions and only on dilute solutions — thiosulfate above a certain level competes for the resin’s sites — and it costs, in Kodak’s own table, between ten thousand and a hundred thousand dollars.

!What each method hands you, and why it decides the domestic answer

Kodak’s refining publication tabulates the silver content of the object each route produces, by dry weight:

Route	What you hold	Silver content
Electrolysis	Greyish-brown metallic flake	above 90 %
Metallic replacement	A dark liquid sludge in a spent cartridge	20 to 40 %
Precipitation (TMT)	A light green to yellow sludge	50 to 70 %
Ion exchange, regenerated in situ	Black swollen beads	40 to 60 %
Ion exchange, eluted	Green wet sand	2 to 4 %

A refiner charges three ways — a retainment charge for assay inaccuracy, a treatment charge that is higher for the more labour-intensive materials, cartridge sludge among them, and a refining charge — and Kodak states plainly that a cartridge run badly or changed too often “may contain so little silver that the refining costs exceed the value of the silver”. Its technology sheet says the same thing about the method in general: “frequently the recovered silver barely pays for the materials and equipment used to collect it.”

The cheapest method to buy produces the poorest material to refine. That is not an accident of pricing; it is because iron dissolves into the same sludge the silver settles into.

What is realistic in a house

Kodak’s guidance for amateurs is unusually direct, and it is the closest thing in the corpus to advice addressed to this course’s reader. Metallic replacement is “usually a good method” for small-volume users, in a cartridge costing about fifty United States dollars at the time of writing, connected by a few plumbing fittings, filled with water before first use so the solution meets the greatest surface area of steel wool and does not channel, and used for fixer and bleach-fix only — developer or anything else destroys it. It lasts about six months for an amateur regardless of how little goes through it, because photographic solutions corrode steel whether or not there is silver to recover.

Set that against the year’s arithmetic above. Thirty grams of silver, arriving in eight to twenty-six litres, with something like two fifths of it in a print fixer already diluted to 0.5 g/L by the very standard that makes the printer careful — and that fraction of the mass occupying nine tenths of the volume. Two cartridges a year, minimum, by the six-month rule. Sludge at 20 to 40 per cent silver, attracting the highest treatment charge a refiner levies, and a refiner who will want a shipment worth handling.

=The honest conclusion, and what the course cannot tell you

Recovery at domestic scale is an environmental act, not an economic one. Every element of that sentence is sourced: Kodak says an amateur is not required to recover silver, that recovery nonetheless conserves a resource, that the sludge is the poorest material to refine, and that the return frequently barely covers the materials.

What the course cannot tell you is the money. It holds no dated silver price, and a price read today would be wrong by the time you read this page; it also holds no United Kingdom refiner’s minimum lot size or schedule of charges, which is the figure that actually decides the question at thirty grams a year. Those two numbers, dated, would close it, and the planner records the same kind of gap in the same way rather than guessing.

What follows practically is that the realistic domestic route is the one the course has been building since Part II: collect it, label it, and hand it to somebody equipped to deal with it. The silver-bearing waste procedure is that route written down. The experiment that follows this page runs metallic replacement in a jar, and it is worth running for what it shows about redox and about the limits of a bench test — not because it is going to pay for your paper.

The other four streams

Silver dominates this page because it is the only recoverable thing in the darkroom. It is not the only thing that leaves.

Five streams, four destinations, and the one question that is local

1. 1Spent developer — alkaline, organic, oxygen-demandingNegligible silver, so nothing to recover and every reason not to tip it into the fixer bottle where it would spoil a solution that does carry silver. Typical photographic effluent runs 100 to 1,000 mg/L of five-day biochemical oxygen demand against a mean regulated 350. The hydroquinone entry carries H400 in almost every notification.
2. 2Spent stop bath — acid, and never near the fixer bottleKodak recommends neutralising its indicator stop bath before discharge, with bicarbonate added slowly because it foams, in a ventilated place, in gloves, goggles and an apron. Neutralisation fixes pH and nothing else.
3. 3Spent fixer and the first wash — the silverEverything above. One container, one route, one label.
4. 4Later wash water — large volume, very diluteKodak gives 1 to 5 mg/L for a developing-out wash; the EPA guide gives 1 to 50 mg/L for spent rinsewater and says up to 10 per cent of the recoverable silver arrives there by carry-over even with a squeegee and a working recovery unit. Too dilute to recover economically, not obviously dilute enough to ignore.
5. 5Toners, and the one that is differentIn Kodak’s own table of routes for its own products, used Rapid Selenium Toner is the single entry with every route withheld except household hazardous waste collection: no sewer, no treatment works, no trash. The selenium entry carries the argument.

The chemistry that decides each row does not change with jurisdiction. Where the row ends up does.

Two of those rows have pages of their own and are not restated here: the hydroquinone entry sets out the developer stream’s aquatic classification and the tension inside ILFORD’s own guidance about flushing dilute working solutions, and the selenium entry sets out why the toner is the one product both manufacturers single out. Part II owns the containers and the log. And the rule that makes the diagram a diagram rather than a list is on the incompatibility matrix: acid into thiosulfate gives sulfur dioxide, at once, in a sealed bottle you are leaning over.

Where the law comes into it, and where it stops

The course settles this once, in the disposal caveat, and every waste section in every part cites that page rather than restating it. What belongs here is the part specific to silver, and one comparison the disposal page does not draw.

Classification, in Great Britain, does not depend on how dilute the bottle is. The Environment Agency’s List of Waste puts photographic developer, fixer and bleach-fix solutions under absolute hazardous entries in chapter 09, and separately collected household photochemicals under 20 01 17* in chapter 20, which is also absolute hazardous. An absolute hazardous entry always applies, must be used, and applies even where the waste displays no hazardous property. So the carefully-discarded 0.5 g/L print fixer is classified exactly as the 9 g/L film fixer is, and no threshold has to be computed by anyone.

In the United States the domestic case is explicitly outside the industrial rules. The federal effluent guidelines for photographic processing, 40 CFR Part 459, exclude facilities processing 150 square metres a day or less, which is every darkroom this course describes; Kodak states that a domestic user is excluded from the pretreatment codes; and the EPA’s own household guidance points the reader at a local environmental, health or waste agency. That is a pointer, not an answer.

In the United Kingdom the reader is a household until they sell a print. Section 118 of the Water Industry Act 1991 makes trade effluent from trade premises a matter of consent from the sewerage undertaker, and discharging without consent an offence. The trade effluent distinction is not academic for a course whose students sometimes start selling work.

!Two manufacturers, two countries, two different instructions, one reader

This is the comparison that makes the caveat impossible to dismiss as boilerplate.

Kodak, writing for amateurs in the United States, lists developers, stop baths, fixers after silver recovery, and wash waters among the things that may be sent to a sewer served by a treatment works, and withholds only selenium toners, solvents and flammables.

ILFORD, writing for domestic users in the United Kingdom, directs that used chemistry be bottled separately, labelled, and taken to a household waste and recycling centre.

Neither is wrong. They are answering the same question in two jurisdictions with different sewer regimes, different classification systems and different collection infrastructure — and the British one has a provision, section 111 of the Water Industry Act 1991, that binds any person rather than only trade premises. The United Kingdom government’s own service for finding a household hazardous waste route states on its face that it covers England and Wales only: two of four nations, on one page.

What this course does, and why. It collects everything, in labelled containers, and applies the standing caveat. That is the conservative choice, it costs a bottle and a shelf, and it is the only choice that is correct in both jurisdictions at once. It is not a claim that the other advice is unsafe; it is a recognition that a page written in one place cannot know which set of rules its reader is under.

What this part’s own streams add, and what the course still could not source

Two silver-bearing streams reach this container from outside the ordinary darkroom sequence, and the disposal page now carries the ruling on both, so it is applied here rather than argued again.

The first wash from the printing-out processes — salted paper, albumen, Van Dyke — carries more silver than anything in Parts VIII to XII, and it carries it in the first wash rather than the fixer, because the sensitiser holds an excess of soluble silver nitrate that water removes. It is collected as a silver-bearing stream, into the same container as spent fixer, and routed as photographic chemistry. What no source in this course’s corpus gives is a measured concentration for that wash. Kodak’s 1 to 5 mg/L is a developing-out figure and the course refuses to transfer it. A measurement from a named sensitiser at a stated coating weight would close it, and the course would publish it.

Chromium(III) from the emulsion coating station, where a lesson uses chrome alum as an in-emulsion hardener, changes what must be written on the container and not the classification of what is in it, because the List of Waste code is chosen by source rather than by composition. The chromium policy carries the rest, including the point that the course’s default is no hardener at all.

Record keeping, and the line that closes a session

None of the above works without a number you wrote down, and the number the recovery question needs is not “how much waste” but which process the silver came from. Thirty grams a year is an answer to a stated workflow, not to yours.

📓What the log has to carry for this page to be usable

The waste-log line already asks for date opened, stream, container and size, date closed, running volume, route and the date the route was checked. Two columns turn it into evidence rather than housekeeping:

Source process, so that film fixer, print fixer and printing-out first wash can be told apart in the total — because they arrive at wildly different concentrations and only one of them is worth recovery at any scale.

Work through the bath, in rolls or in 8 × 10 equivalents, taken from the capacity log the fixing criterion already requires. That is what converts a volume into a mass, using the per-film and per-print figures above, without any instrument at all.

Then the annual re-check the disposal page asks for: authority, URL, date. Ten minutes, once a year, and after any move.

The lab-closing procedure is where this becomes a habit rather than an intention, and the container-labelling procedure is why a full bottle is something a waste service will accept rather than an unknown it will refuse.

Recap

A home darkroom’s spent fixer runs at grams of silver per litre where a mean sewer limit is milligrams, and the stated workflow above produces about 30 g a year in 8 to 26 litres — most of the volume from print fixer discarded early for permanence, which is the careful printer’s penalty. Industry takes silver back four ways: electrolysis, which is efficient and stops at a few hundred milligrams per litre; metallic replacement, which is cheap, reaches below 5 mg/L and discharges iron; precipitation, which reaches lowest and which the industry abandoned in its classical sulfide form on hazard grounds; and ion exchange, for wash water and at industrial cost. Each hands you a different object, and the cheapest method produces the poorest one to refine — which is why domestic recovery is an environmental act rather than an economic one, and why the realistic route is collection under a labelled, dated, logged scheme. The classification of the bottle does not soften with dilution, the two major manufacturers give domestic users different instructions in different countries, and the sentence at the end of every waste section in this course is doing real work: the chemistry is general, the law is local, it changes, and you must check your local regulations.

Check your understanding

Question 1. A printer makes sixty 8 × 10 fibre prints a month and exposes one roll of 135-36 a month, holding prints to ILFORD’s maximum-stability ceiling of about ten prints per litre of fixer. Roughly how much silver reaches the fixer in a year, and roughly how many litres of spent fixer does it arrive in?

• About 36 g in about 72 L
• About 40 g in about 73 L
• About 4 g in about 8 L
• About 400 g in about 700 L

Show the answer and why

Answer: About 40 g in about 73 L

Prints: 60 × 12 = 720 prints a year at 50 mg each is 36 g, and at ten prints per litre that is 72 L. Films: 12 rolls at 0.33 to 0.42 g is 4 to 5 g, and at 24 rolls per litre that is half a litre. Totals: about 40 to 41 g in about 72.5 L, so 40 g in 73 L. The point of the arithmetic is the shape rather than the digits — the print work dominates both the mass and, overwhelmingly, the volume, and the average concentration works out near 0.5 g/L, which is still some four hundred times a mean regulated sewer limit of 1.2 mg/L.

Question 2. Why does pushing an electrolytic silver-recovery cell to desilver below about 200 mg/L make it work worse rather than better?

• The cell overheats and the thiosulfate decomposes to sulfur
• Below that concentration the cathode plates a black, crumbly, silver-sulfide-contaminated deposit instead of clean flake, which drops the cell’s efficiency
• The anode stops oxidising sulfite, so the pH falls out of range
• Silver redissolves in the thiosulfate as fast as it plates, so nothing is gained

Show the answer and why

Answer: Below that concentration the cathode plates a black, crumbly, silver-sulfide-contaminated deposit instead of clean flake, which drops the cell’s efficiency

Kodak describes the failure exactly: extending residence time or raising current density to reach lower concentrations produces an inferior, black, crumbly plate contaminated with silver sulfide, and the cell’s efficiency falls dramatically. It is a mass-transfer problem — starved of silver at the cathode surface, the current finds something else to do, and sulfide is what forms. That is why electrolysis is a primary treatment and needs a tailing stage after it, and why ILFORD warns that vigorous electrolysis can release hydrogen sulfide.

Question 3. A metallic replacement cartridge is fed a fixer that has been over-acidified to about pH 3. What goes wrong?

• The silver plates as an oxide instead of the metal
• The steel wool dissolves far faster than the displacement needs, so the cartridge’s capacity is consumed without recovering the silver it was bought to recover
• The reaction stops, because iron will not reduce silver below pH 5
• Hydrogen sulfide is released from the thiosulfate and the cartridge must be discarded

Show the answer and why

Answer: The steel wool dissolves far faster than the displacement needs, so the cartridge’s capacity is consumed without recovering the silver it was bought to recover

Kodak gives an ideal range of pH 5.5 to 6.5 and states that below pH 5 the steel is catalysed to dissolve too rapidly and the capacity of the cartridge can be significantly reduced; its small-volume sheet puts the workable band at 4 to 6.5 and says a bath below pH 4 dissolves the wool so that it is unavailable for silver replacement. Above pH 7 the opposite failure appears — the dissolution is too slow and silver passes through. The reaction needs iron to be oxidised, and the acid decides how fast that happens with or without silver present.

Question 4. Kodak states that the silver in photographic effluent exists as a thiosulfate complex which is not toxic, and also that silver should be recovered before discharge. Which reading of those two statements is the one this course takes?

• The toxicity statement is outdated and the recovery advice supersedes it
• They address different things — species and stream — so both stand: sewer codes and the aquatic hazard statements regulate total silver regardless of what it is bound to, and the course collects rather than choosing a side
• The recovery advice is commercial, since Kodak sold recovery equipment, so the toxicity statement is the reliable half
• The complex decomposes to free silver ion in the sewer, so the toxicity statement is wrong

Show the answer and why

Answer: They address different things — species and stream — so both stand: sewer codes and the aquatic hazard statements regulate total silver regardless of what it is bound to, and the course collects rather than choosing a side

Distinguishing fact from interpretation is a house rule, and this is a case where two sourced statements look contradictory and are not. A hazard classification attaches to a substance; a discharge limit attaches to a stream and is written as total silver; and free silver ion, which is what is acutely toxic to micro-organisms, is not the same species as the complex. The fourth option is the tempting one and the course does not assert it, because no source in the corpus establishes what the complex does downstream of a particular works. Collecting is the choice that is correct whichever way that unresolved question falls.

Question 5. Why does a very dilute rinse collected from a printing-out sensitiser still go into the silver-bearing container in Great Britain, rather than being judged on its concentration?

• Because its silver concentration has been measured and exceeds 5 ppm
• Because the List of Waste identifies the waste by its source and the relevant entries are absolute hazardous, so the entry applies whatever the concentration and even if the waste shows no hazardous property
• Because all liquids containing any silver are hazardous waste everywhere
• Because the Hazardous Waste Regulations impose a duty on the occupier of domestic premises to separate it

Show the answer and why

Answer: Because the List of Waste identifies the waste by its source and the relevant entries are absolute hazardous, so the entry applies whatever the concentration and even if the waste shows no hazardous property

This is the finding that answered a question the printing-out labs kept asking. WM3 identifies waste by source at the first step, and both candidate entries — chapter 09’s photographic-industry solutions and chapter 20’s 20 01 17* photochemicals — are absolute hazardous, which means the entry always applies, must be used, and applies even where the waste has no hazardous property. So there is no threshold for a lab page to compute. Note what the correct answer does not say: it is a classification in one jurisdiction, not a permission or a prohibition about what may then be done with the bottle, and no measured silver figure for a printing-out first wash exists in this course’s corpus at all.

Question 6. Of the four recovery methods, metallic replacement is the cheapest to buy and reaches a lower final silver concentration than electrolysis. Why is it nonetheless the least attractive material to send to a refiner?

• The sludge is 20 to 40 per cent silver, the poorest of the recovered forms, and its labour-intensive handling attracts the highest treatment charge
• Refiners will not accept iron-bearing material at all
• The silver in the sludge is a sulfide rather than the metal and needs a separate reduction step
• The cartridge cannot legally be transported without a hazardous waste manifest

Show the answer and why

Answer: The sludge is 20 to 40 per cent silver, the poorest of the recovered forms, and its labour-intensive handling attracts the highest treatment charge

Kodak’s refining sheet tabulates it: electrolytic flake above 90 per cent silver, TMT precipitate 50 to 70, in-situ regenerated resin 40 to 60, and cartridge sludge 20 to 40 — because the iron that did the reducing ends up in the same sludge. The refiner’s treatment charge is higher for the more labour-intensive materials, cartridge sludge among them, and Kodak states that a cartridge run badly or changed too often may hold so little silver that refining costs exceed its value. The cheapest equipment produces the most expensive material to process, which is the whole reason the domestic answer is collection rather than recovery.

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