chemical fixation

Incorrect. Chemical fixation aims to reduce the concentration of harmful substances.

Correct. Chemical fixation aims to change harmful compounds into less toxic or inert forms.

Incorrect. While decomposition can be a part of some treatment processes, chemical fixation focuses on transformation rather than decomposition.

Incorrect. Dilution does not eliminate the hazard; chemical fixation aims to remove or neutralize it.

Incorrect. Chemical fixation is used for heavy metal removal.

Incorrect. Chemical fixation is used for organic pollutant removal.

Correct. Chemical fixation is not directly used for waste management. While it can be used to treat some waste components, it is not the primary method for waste management.

Incorrect. Chemical fixation is crucial for wastewater treatment.

Incorrect. Oxidation/reduction changes the chemical structure, not necessarily forming a precipitate.

Incorrect. Stabilization involves incorporating the compound into a stable matrix, not forming a precipitate.

Correct. Precipitation is the process of forming a solid precipitate by reacting the target compound with a reagent.

Incorrect. Adsorption involves the attachment of a substance to a surface, not forming a precipitate.

Incorrect. While the goal is to minimize toxicity, not all fixation methods create completely inert compounds.

Incorrect. Cost can be a limitation, depending on the complexity of the contaminant and reagents.

Correct. The transformed compounds are generally stable and less likely to leach back into the environment, providing long-term protection.

Incorrect. Chemical fixation is versatile but not applicable to all types of pollutants.

Incorrect. Chemical fixation can be applied to both organic and inorganic pollutants, including heavy metals.

Correct. While minimizing toxicity is the goal, some fixation methods may create new compounds that need additional treatment.

Incorrect. Chemical fixation is particularly effective in removing heavy metals.

Incorrect. Chemical fixation is applied in various settings, including industrial and wastewater treatment plants.

Here's a possible solution:

**Reagent:** The most suitable reagent for lead precipitation is **sodium sulfide (Na₂S)**. Sodium sulfide reacts with lead ions in the wastewater to form lead sulfide (PbS), an insoluble precipitate:

Pb²⁺ (aq) + Na₂S (aq) → PbS (s) + 2Na⁺ (aq)

**Reaction Conditions:** The reaction should be carried out at a slightly alkaline pH (around 8-9). This ensures that the sulfide ions remain in solution and react effectively with lead ions. The reaction can occur at ambient temperature, though slightly elevated temperatures might slightly increase the reaction rate.

**Safe Disposal:** The precipitated lead sulfide should be collected, dried, and disposed of in a **hazardous waste landfill**, following local regulations. It's crucial to prevent the lead sulfide from re-entering the environment.

**Additional Considerations:**

• It's important to monitor the lead concentration in the wastewater after treatment to ensure that the process is effective and meets safety standards.
• Alternative reagents like calcium hydroxide or sodium hydroxide can also be used for lead precipitation, but they may require different reaction conditions.
• The scale of the operation and the volume of wastewater will determine the amount of reagent required and the size of the treatment system.