Purification of sewage water from heavy metals using bone meal

The purpose of the study was to examine if different types of bone meal can absorb heavy metals from a synthetic metal solution. Four kinds of metals were studied. They were cadmium (Cd) in the form of cadmium chloride, lead (Pb) in the form of lead nitrate, mercury (Hg) in the form of mercuric nitrate dehydrate and chromium in the form of chromium chloride hex hydrate. Three different sorts of bone meal were examined; they were calcium phosphate (CAP meal), meat and bone meal (MBM) and decanter cake (DC). All the meal-types had in common that they reduce heavy metals very well. Generally cadmium and lead are reduced better at around 99 percent, while the reduction for mercury and chromium is somewhat lower, between 90 and 99 percent. The reduction is of course dependent on how the test is carried out and which bone meal is used. The binding is best explained by three mechanisms depending on which metal that is bound. The binding can occur though an ion-exchange mechanism, an adsorption mechanism or through binding to the proteins in the bone meal. Most likely the binding of the different metals occurs through a combination of all these mechanisms. All the types of bone meal that were examined would work perfectly as a product for purifying for example sewage water. The CAP meal is the type of bone meal that has been examined most closely. The binding is fast and effective, bound metal is kept even after a long period of time and the bone meal also works fine at continuous operation. Even to MBM the binding is fast and effective. For DC the binding takes somewhat longer, but the reduction is in the end very good, especially when it comes to mercury, where the reduction is 99 percent