Germanium and solid sample digestion with aqua regia: the nescience of chemistry basics and its sequels

The role of germanium in technology is steadily growing in importance, bringing in its wake an increased attention to its concentration and behaviour in the environment. A recent study on European agricultural soils reported that only 1% of Ge in soils was released when treated with aqua regia, a rather surprising result. The investigation of possible causes showed that huge Ge losses, as were observed in the aforementioned study, are likely to result when the sample is digested in an open system, because of the well-known volatility of the GeCl4 formed. Our study also reveals that, when working in a semi-closed system, replacement of HNO3 by NaOH in the absorbing solution is needed for complete Ge recovery. The underlying rationale has been explored by calorimetry. This case shows that widely used techniques embedded in many current, accepted environmental methods, such as aqua regia extraction, cannot be applied blindly but rather require the consideration of fundamental chemical knowledge