Naval Jelly, a rust remover made by the Henkel Corporation, contains phosphoric acid. Like any product that contains an acid as an active ingredient, follow certain precautions for its storage and handling. While the precautions for handling the product are listed on the container, it's possible that you will find it necessary to neutralize the Naval Jelly--possibly you spilled some, or it dripped onto your patio while you were stripping the paint off of a wrought iron fence or furniture or you might be the first responder to an environmental spill. Whatever the reason, the instructions in the Material Safety Data Sheet for Naval Jelly are specific.
Neutralize the Naval Jelly with soda ash or lime. Naval Jelly uses phosphoric acid to strip rust from metal. Soda ash and lime are both "base" compounds, which neutralize acids.
Both soda ash and lime can be found in garden shops, where they're sold for use in gardening. Both come in a powdered form and can be shoveled onto the Naval Jelly.
Spread an inert material, such as sorbalite clay, blanketing the Naval Jelly completely. Sorbalite clay is used to make some kinds of cat litter and industrial oil absorbents. It absorbs the moisture in the Naval Jelly quickly.
Use the shovel to deposit the Naval Jelly, now in a mud-like form, into an approved hazardous waste disposal container.
Flush the area with running water from your garden hose, at full pressure, for at least 15 minutes. Adding water in large quantities dilutes any remaining phosphoric acid in the Naval Jelly to about 0.0000185:1, and removes the threat that the acid might prevent. Because of the level of dilution, Naval Jelly is no longer considered hazardous to the environment.