Sulfide precipitation of metals is typically regarded as:

Sulfide precipitation of metals is often recognized as a method that can be more expensive than hydroxide precipitation due to various factors involved in the process. This type of precipitation typically requires the addition of sulfur compounds, which may incur higher material costs and necessitate more complex operational procedures, including the need for specific equipment designed to manage toxic sulfides safely.

Additionally, the handling and disposal of sulfide wastes can contribute to increased operational expenses. The conditions required for effective sulfide precipitation, such as controlled pH levels and temperature, may also add to the overall process costs.

In contrast, hydroxide precipitation is generally considered a more conventional and straightforward approach for metal removal in wastewater treatment, often resulting in lower costs associated with both materials and process management. This makes the application of sulfide precipitation less favorable from a cost perspective when compared to hydroxide precipitation methods.

Therefore, the premise that sulfide precipitation is more expensive aligns with common industry practices and considerations regarding the economics of wastewater treatment processes.