What process can remove over 90% of sodium arsenate from water?

The most effective process for removing over 90% of sodium arsenate from water is ion exchange. This method specifically targets and removes certain ions from a solution and is particularly effective at dealing with charged contaminants such as heavy metals and arsenates. In ion exchange systems, sodium ions from the water are exchanged for arsenate ions bound to the exchange resin. This process can significantly reduce arsenate levels, often achieving over 90% removal efficiency.

Coagulation, while it can be effective for removing particles and some dissolved substances from water, typically does not achieve the high levels of specific ion removal that ion exchange does. Filtration can also help in removing some contaminants but is generally not as adept at selectively removing dissolved ionic species like sodium arsenate compared to ion exchange.

Thus, the effectiveness of ion exchange in targeting sodium arsenate specifically justifies its identification as the correct process.