El medio ambiente en la minería

97 ANGELSELKE Basical1yhidrogen sulphide is used as precipitation agent, but to achieve a very lowarsenic content ofless than 0.5 ppm under large scale operating conditions a small amount of hidrogen sulphide ions are added lo the reactor as well. The filter cake contains the precipitated arsenic sulphide, other suspended solids from the treated acid and filter aids. The fIlter cake has a high solids content ofmore than 50% and can easily be handled.. In Germanythis filter cake is considered as specialwastewhich has to be stored in an underground safely disposal. Therefore the filter cake is filled into steel drums which are lined with plastic foil. The treated washing acid contains dissolved hidrogen sulphide which has to be removed by stripping with airo The off-air containing 1 to 1.5% volume of hidrogen sulphide is bumt replacing combustion air or other process sections. After the stripping, the washing acid contains less than 0.5 ppm arsenic. Figure 11 - Comparison of tbe arsenic removal by neutralizationwith lime and the Sachtleben-Lurgi-Process. The Sachtleben plant in Duioburg-Germany is in operation for more tban five years. The plant is incorporated into the sulpburic acid production facility. The arsenic removal plant is operated by one operator.