Which method can often remove over 90% of sodium arsenate?

Coagulation is an effective method for removing contaminants such as sodium arsenate from water. This process involves the addition of chemicals to water that cause particles to clump together, forming larger aggregates that can be more easily removed. In the case of sodium arsenate, coagulation is particularly effective because the arsenate ions can be trapped within the larger aggregates formed during the process. This allows for high removal efficiencies, often exceeding 90%.

While filtration and ion exchange can also be useful methods for removing various contaminants, they may not specifically target sodium arsenate as effectively as coagulation does. Filtration works by physically separating particles from the fluid, but it may not be as efficient for dissolved ions like arsenate unless specifically designed for that purpose. Ion exchange is another technique that can remove certain ions by swapping them with others on a resin, but it may require more specific conditions and may not guarantee the same high removal rates for sodium arsenate as coagulation does.

Thus, coagulation stands out in this context as a highly effective method specifically for reducing sodium arsenate concentrations in water.