Accessibility and Transparency
Public blockchain is open to the public. where as Private blockchain are limited access and viewability is restricted to authorized personnel.
Governance
Public blockchains are Permissionless governance, where as private blockchains are Permissioned governance
Consensus
Public blockchains use Proof of Work (PoW) or Proof of Stake (PoS), where as private blockchain uses Proof of Authority (PoA).
Scalability
Public blockchains have scalability issues, where as private blockchain are highly scalable.