Can I use the attach/detach database option to shut down Azure sql database until i need it I need to use Azure SQL Database once a week for a BI solution.  O load the data in on Monday, perform ETL, and then load the data into a PowerBI model.  After that I don't need the database anymore until next week.  In order to save costs can I just detach the database and attach next week?
No. Attach/detach are not supported on Azure SQL DB. A few workarounds today:


Change the pricing tier (performance level) to the lowest that can support your database (each tier has a certain size limit), you can bring it up to the require performance level when you need to use it
Export to Azure blob (very low cost storage) when not needed, import when needed later (ok for smaller databases). More information on this at https://docs.microsoft.com/en-us/azure/sql-database/sql-database-export 
Delete the database when not needed, restore later. Not recommended but you'll see this suggestion come up quite a bit. Be careful not to delete the server (costs you nothing if you don't have DBs in it) and depending on the pricing tier of the database, backup retention varies from 7 to 35 days. If it's past the period, you're pretty much out of luck. See difference between export/import and backup/restore here https://azure.microsoft.com/en-us/blog/azure-sql-database-built-in-backups-vs-importexport-2/