This technical note focuses on heavy. metal soil contamination. Metals in Soil. Mining, manufacturing, and the use of synthetic products (e.g. pesticides, paints, batteries, industrial waste, and land application of industrial or domestic sludge) can result in heavy metal contamination of urban and agricultural soils.
As a beginner, try practicing the guitar for 10-15 minutes a day. As you begin to build your finger muscles and improve your playing, you can increase this amount of time as you see fit. You may feel comfortable practice for 30 minutes per day, an hour per day, or even more.
It all depends on how you define learning. If all you want to do play a steady basic rock 12 hours is more than sufficient, but If you want to go beyond that to be able play at least half as good as legends like Buddy Rich, Terry Bozzio , Gene Krupa , Neil Peart etc it would take a lot more than that.