Environmental Chemistry

1 Chapter overview

This chapter is the chemistry of consequences: what nuclear and chemical industries leave behind, and what chemistry does about it. You will classify radioactive wastes (LLW / ILW / HLW) by activity, see why glass is the universal matrix for their disposal, work with glass fertilizers — the slow-release answer of the fertilizer industry — and cover the environmental-chemistry staples the paper keeps asking: green chemistry and atom economy, energy resources, electroplating, galvanization, and industrial pollution management.

Roadmap

• §2 Concepts — waste nature and classification, glass chemistry (vitrification, fertilizers), green-chemistry principles, energy resources, and the short industrial topics (microwave digestion, electroplating, galvanization, paper & pulp, petroleum, LPG odorant).
• §3 Derivations — the % atom-economy formula with the ethyl propionate + methyl amine case worked, and the activity-based waste-classification logic.
• §4 Examples — the atom-economy numerical verified step by step, a real sample glass-fertilizer composition, electroplating cell setups, LLW-vs-HLW by activity, and the India energy-mix pie.
• §5 Figures — waste-treatment flowchart, glass-fertilizer pH/weight-loss vs time, worldwide + India energy diagrams.
• §6 PYQ bank — all 29 questions, 2020–2024, with full solutions.

2 Core concepts

2.1 What constitutes nuclear waste?

Nuclear (radioactive) waste is any material containing radionuclides at concentrations above the clearance levels set by the regulator, for which no further use is foreseen. It is not only "spent fuel": it includes

• fission products from reprocessing ($^{137}Cs$, $^{90}Sr$, $^{99}Tc$) — the bulk of the activity,
• transuranics (Pu, Am, Np) and minor actinides — the bulk of the long-term radiotoxicity,
• activation products ($^{60}Co$, $^{63}Ni$) from reactor structures and coolants,
• contaminated operational waste — gloves, clothing, filters, resins, tools, decontamination liquors.

Sources: power reactors, fuel fabrication, reprocessing plants, research reactors, hospitals and industry (sealed sources). Hazardous (non-radioactive) chemical waste is classified separately by its properties: ignitable, corrosive, reactive, toxic (heavy metals such as Hg, Pb, Cd; chlorinated organics; PCBs) — the exam occasionally pairs the two, so keep the one-line definition.

2.2 Classification of radioactive waste by activity

The IAEA scheme (Safety Guide GSG-1) classifies waste by activity content and half-life, which fixes how long it must be isolated and how deep it must be buried. The exam's favourite formulation is "differentiate LLW and HLW in terms of their activity":

Boundary markers to memorise: the 2 kW m⁻³ heat criterion separates ILW from HLW; HLW's activity concentration is roughly a million times that of typical LLW. Below LLW sit VLLW (very low level) and exempt waste; VSLW (very short-lived) is simply stored for decay.

2.3 Treatment and management of nuclear waste

Management follows a fixed chain — segregate → treat → condition → store → dispose:

• Volume reduction — compaction, incineration, evaporation of liquid LLW/ILW.
• Conditioning (immobilisation) — fixing the waste in a stable solid matrix: cementation (LLW/ILW), bituminisation (historical, fire-risk concerns), and vitrification (HLW — the exam topic).
• Interim storage — engineered stores (e.g. India's Solid Waste Storage Facility at Tarapur) let heat and activity decay before final disposal.
• Disposal — near-surface engineered trenches/vaults for LLW; intermediate-depth facilities for ILW; a deep geological repository (stable rock, multi-barrier: glass + canister + backfill + host rock) for HLW.

2.4 Glass chemistry for vitrification — oxides by function

The 2020 paper asked to classify glass component oxides by function. The three roles:

2.5 Advantages of HLW fixation in glass

• Permanent, irreversible fixation — radionuclides become part of the glass structure; they cannot be washed out by a simple solvent.
• Very low leachability — dissolution/leach rates are orders of magnitude below regulatory concern, giving the waste form a service life of thousands of years in a repository.
• High waste loading with wide compositional tolerance — the amorphous network swallows fission products, actinides and process chemicals together.
• Volume reduction — liquid HLW is concentrated and turned into compact glass logs in stainless-steel canisters.
• Radiation and thermal stability — the glass does not decompose under its own decay heat or radiation field.
• Suppression of volatile release — semi-volatiles (Cs, Ru, Tc) are trapped in the melt rather than escaping as gas.

2.6 LIP glasses — distinct advantages

LIP = lead–iron–phosphate glasses ($PbO$–$Fe_2O_3$–$P_2O_5$ system), investigated as an alternative to the borosilicate reference. Their distinct advantages, reported in the literature (not shared by borosilicate):

• ~1000× lower dissolution rate in water than comparable borosilicate formulations (measured at 90 °C, pH 5–9) — iron addition alone raises durability by about $10^4$ at ~9 wt% iron oxide;
• processing temperature 100–250 °C lower (melts form at ~800–950 °C) and much lower melt viscosity in the 700–1000 °C range, easing melter operation;
• good tolerance of waste streams rich in phosphorus, fluorides and heavy-metal oxides that are poorly soluble in borosilicate glass.

2.7 Latest technology: immobilisation and disposal through the glass route

The exam asks this every other year — the answer is the melter technology plus the disposal system:

• India (BARC): HLW is vitrified in borosilicate glass using induction-heated metallic melters at the Waste Immobilisation Plants (Tarapur, Trombay, Kalpakkam). The glass is poured into stainless-steel canisters, which are stored in the engineered Solid Waste Storage Facility (interim storage) pending a deep geological repository.
• World practice: France (AVM/AVH at Marcoule and La Hague), the UK (WVP at Sellafield) and the USA (DWPF at Savannah River) run Joule-heated ceramic melters; the newest generation is the cold-crucible induction melter (CCIM) — water-cooled, skull-melt operation that tolerates corrosive melts, allows higher waste loading and greatly extends melter life.
• For lower-activity wastes, in-container vitrification (e.g. GeoMelt-type) vitrifies waste directly inside its disposal container — no separate melter needed.

2.8 Glass fertilizers — composition and the 'secular' behaviour of glass

Nutrients in a fertilizer are conventionally divided as:

• Macronutrients — primary: N, P, K; secondary: Ca, Mg, S (needed in % of plant dry matter);
• Micronutrients — Fe, Mn, Zn, Cu, B, Mo, Cl (needed in ppm). Glass fertilizers can carry all except nitrogen, which will not stay in a glass melt.

Sample composition (phosphate system). A commercial phosphate glass fertilizer declares approximately: $P_2O_5$ 14% (6.2% P), $K_2O$ 31% (27.5% K), CaO 19%, $SiO_2$ 28%, $Na_2O$ 2.1%, plus trace elements — research formulations use the $P_2O_5$–$K_2O$–CaO–MgO base with Fe, Mn, Zn, B, Cu, Mo added as oxides (see §4 for the worked table).

The 'secular' behaviour of glass. "Secular" here means slow, steady and long-term: a glass particle does not dump its contents at once — it dissolves congruently and gradually, forming fresh pores as it leaches. Because the release profile follows the chemical durability of the glass, the formulator can manipulate macro- and micronutrient concentrations in two ways: (i) by the batch composition (how much of each oxide goes into the melt — the melt inventory is the nutrient inventory), and (ii) by the release rate, tuned with durability modifiers — $Al_2O_3$ and $Fe_2O_3$ increase durability (slower release), alkali oxides decrease it (faster release). This is what makes a single glass grain a controlled-release, multi-nutrient fertilizer.

pH and weight loss vs time (the 2024 graph question): weight loss of the glass rises with time — fast initially, then nearly linear as steady dissolution sets in — while the leachate pH shifts (phosphate glasses typically drift slightly acidic) and then plateaus once the dissolution front stabilises. The figure is drawn in §5.

2.9 Chemical vs bio fertilizers; fertilizers vs manures

Fertilizers vs manures: fertilizers are concentrated, industrially made nutrient sources of defined composition acting quickly; manures (farmyard manure, compost, green manure) are bulky organic materials of low, variable nutrient content that improve soil structure, water-holding and microbial life while releasing nutrients slowly.

Advantages of glass fertilizers over conventional fertilizers: (i) controlled, slow release over 1–3 years — one application per crop cycle or less; (ii) no leaching into groundwater, so no nitrate/phosphate pollution and no crop "burning"; (iii) macro- and micronutrients delivered in a single matrix; (iv) no salinisation of soil; (v) up to ~70% cost saving claimed by manufacturers versus repeated conventional dressings.

2.10 Energy resources

Renewable vs non-renewable examples (asked 2022, 2024): renewable — solar, wind, hydropower, biomass, geothermal, tidal; non-renewable — coal, petroleum, natural gas, uranium (nuclear fuel).

Worldwide picture (indicative, IEA total primary energy supply ≈2022–23): oil ≈ 31%, coal ≈ 27%, natural gas ≈ 24%, nuclear ≈ 5%, hydropower ≈ 3%, biofuels & waste ≈ 8%, other renewables (solar, wind, geothermal) ≈ 2%. India's mix (indicative, 2024): coal ≈ 59%, oil ≈ 28%, natural gas ≈ 6%, hydro + nuclear + renewables ≈ 7% — coal remains the backbone (MoSPI notes coal is ~79% of domestically produced energy supply). Both diagrams are drawn in §5; treat every share as approximate.

2.11 Green chemistry — the 12 principles

Anastas & Warner (1998). The exam asks which two are most relevant — the standard answer is (1) Prevention and (2) Atom economy:

1. Prevention — it is better to prevent waste than to treat or clean it up afterwards.
2. Atom economy — synthetic methods should maximise incorporation of all starting materials into the final product.
3. Less hazardous chemical syntheses.
4. Designing safer chemicals.
5. Safer solvents and auxiliaries.
6. Design for energy efficiency.
7. Use of renewable feedstocks.
8. Reduce derivatives (avoid protection/deprotection steps).
9. Catalysis (catalytic rather than stoichiometric reagents).
10. Design for degradation.
11. Real-time analysis for pollution prevention.
12. Inherently safer chemistry for accident prevention.

Justification: this paper's whole theme is waste — its prevention, treatment and disposal. Prevention attacks the problem at the design stage so no end-of-pipe treatment is needed at all, and atom economy is its quantitative measure: it tells, before a single experiment, what fraction of the atoms you buy ends up in the product versus the waste bin. Together they make "waste management" unnecessary rather than merely efficient — which is exactly the hierarchy the syllabus wants.

2.12 Short industrial topics (one PYQ each — learn as facts)

• Microwave digestion vs conventional heating. Sample digestion in closed PTFE vessels: microwaves heat the acid directly by dielectric loss (polar molecules couple to the field), so digestion finishes in minutes instead of hours, at higher temperature and pressure, with no contamination, no loss of volatile analytes, less reagent and lower blanks. Conventional open hot-plate heating is slow, risks contamination and boil-off losses, and needs more acid.
• Electroplating. The article to be coated is always the cathode (negative electrode); metal ions reduce onto it. Ag on Fe: iron plate = cathode, silver (or inert) anode, electrolyte an alkaline silver-cyanide bath — cathode reaction $Ag^+ + e^- \rightarrow Ag$. Au on Fe: iron plate = cathode, gold anode, potassium dicyanoaurate $K[Au(CN)_2]$ bath — $Au(CN)_2^- + e^- \rightarrow Au + 2CN^-$.
• Galvanization = coating iron/steel with zinc (hot-dip). Electrochemically: $E^\circ_{Zn^{2+}/Zn} = -0.76\ \text{V}$ is more negative than $E^\circ_{Fe^{2+}/Fe} = -0.44\ \text{V}$, so zinc is the sacrificial anode — it corrodes preferentially and the iron stays cathodically protected even when the coating is scratched.
• Paper & pulp pollution management. Effluents carry high BOD/COD, suspended solids, lignin, and — from elemental-chlorine bleaching — chlorinated organics (dioxins). Management: black-liquor recovery (kraft recovery boiler), ECF/TCF bleaching (oxygen delignification, ozone, peroxide instead of chlorine), segregation of streams, primary clarification + activated-sludge secondary treatment, water recycling, and air-emission control (TRS gases, particulates) with scrubbers/ESPs.
• Petroleum — major composition: overwhelmingly hydrocarbons — paraffins (alkanes), naphthenes (cycloalkanes) and aromatics — roughly 84–87% C and 11–14% H by weight, plus small amounts of S, N, O compounds and trace metals; separated into fractions (LPG, naphtha, kerosene, diesel, lubricants, bitumen) by distillation.
• LPG dopant: ethyl mercaptan (ethanethiol, $C_2H_5SH$) is deliberately added because LPG itself is odourless; the mercaptan's pungent garlic-like smell is detectable at ppb levels, giving early warning of leaks.

3 Key derivations

D1 · % Atom economy — definition and the exam case

Atom economy measures how many of the atoms you pay for end up in the desired product:

Only the balanced equation is needed — yields, solvents and catalysts are ignored. The exam reaction is amide formation from an ester and an amine:

Molar masses (g mol⁻¹): ethyl propionate $C_5H_{10}O_2 = 102.13$; methyl amine $CH_5N = 31.06$; the desired amide $C_4H_9NO = 87.12$; by-product ethanol $C_2H_6O = 46.07$. Mass check: $102.13 + 31.06 = 133.19 = 87.12 + 46.07$ — balanced. Hence

So about 65.4% of the reactant mass becomes the amide; the rest (ethanol, $34.6\%$) is waste — this is exactly why atom economy is green-chemistry principle #2: it quantifies waste at the design stage. (Full step-by-step verification in §4.)

D2 · Activity-based waste classification — the logic

Classification is not arbitrary: it is driven by how hot (activity), how long-lived, and how heat-generating the waste is, because those fix the engineering:

• Heat is the ILW/HLW boundary: waste generating more than ≈ $2\ \text{kW m}^{-3}$ of decay heat needs active thermal design in its disposal facility — that waste is HLW by definition.
• Activity spans ~6 orders of magnitude: typical LLW long-lived α content ≈ $400\ \text{Bq g}^{-1}$; HLW ≈ $10^8\text{--}10^9\ \text{Bq g}^{-1}$. The exam's "differentiate in terms of activity" is answered by exactly this contrast.
• Volume vs radioactivity inversion: HLW is only a few percent of waste volume but carries >95% of the total radioactivity from nuclear power — which is why it alone justifies vitrification and deep geological disposal.

4 Worked examples

E1 · % Atom economy — ethyl propionate + methyl amine (PYQ 2020, twice)

Step 1 — write the balanced equation and identify the desired product (the amide; ethanol is waste):

Step 2 — molar masses:

• Ethyl propionate $C_5H_{10}O_2$: $5(12.011)+10(1.008)+2(15.999) = 102.13$
• Methyl amine $CH_5N$: $12.011+5(1.008)+14.007 = 31.06$
• N-methylpropionamide $C_4H_9NO$: $4(12.011)+9(1.008)+14.007+15.999 = 87.12$
• Ethanol $C_2H_6O$: $2(12.011)+6(1.008)+15.999 = 46.07$

Step 3 — mass-balance check: $102.13+31.06 = 133.19$; $87.12+46.07 = 133.19$ ✓

Step 4 — atom economy: $\%\ AE = 87.12/133.19 \times 100 = 65.4\%$. Answer: 65.4%. Memorise the pattern: desired-product mass ÷ total reactant mass × 100; solvents and catalysts never enter the sum.

E2 · A sample glass-fertilizer composition (phosphate system)

Below is the declared composition of a real commercial phosphate glass fertilizer (oxide wt%), with each oxide's nutrient role — the pattern the 2023/2024 PYQs want:

Research formulations for wheat use the $P_2O_5$–$K_2O$–CaO–MgO base with microelements Fe, Mn, Zn, B, Cu, Mo added directly as oxides at the melting stage. Exam reading: the melt inventory is the nutrient inventory, and release is tuned by durability — $Fe_2O_3$/$Al_2O_3$ slow it down, alkali oxides speed it up ('secular' behaviour, §2.8).

E3 · Electroplating assemblies — Ag on Fe (2021), Au on Fe (2022)

Rule: the article to be coated is always the cathode (negative terminal); metal ions in the bath reduce onto it.

E4 · Differentiate LLW and HLW in terms of their activity (PYQ 2023)

The answer is a two-row contrast, exactly as in the §2 table: LLW — low activity (limited long-lived content; national long-lived-α criterion ≈ $400\ \text{Bq g}^{-1}$), negligible decay heat, near-surface disposal; HLW — activity ≈ $10^8\text{--}10^9\ \text{Bq g}^{-1}$, carries >95% of the radioactivity though a small fraction of the volume, generates significant decay heat (> $2\ \text{kW m}^{-3}$), and requires vitrification plus a deep geological repository. Add one line: LLW needs isolation for hundreds of years; HLW for thousands.

E5 · Reading the India energy-mix circle (PYQ 2021, 2024)

For a "circular diagram" question: convert each fuel's share of total primary energy supply to a pie angle (share × 360°). Indicative 2024 values: coal 59% → 212°, oil 28% → 101°, natural gas 6% → 22°, hydro + nuclear + renewables 7% → 25°. Always write "indicative/approximate" under the diagram and name the basis (total primary energy supply, not electricity alone — coal's share of electricity is higher). See Fig. 3.

5 Figures

6 PYQ bank

All 29 questions on this chapter from the Burdwan M.Sc. papers (2020–2024), each with year badges and a full solution. Cross-references point to the concept/explanation sections above.

7 Exam Q&A

8 Quick revision